Here are a few things.
1. Impulse did not create any desktop icons at all (other than for itself). I had to manually create one for Titan Quest and have yet to do so for Dawn of War - Dark Crusade.
2. I Archived the games but I have no idea what that really did or what it really means. The little Help ? was of little help answering this question.
3. To not have Impulse running is fine, but I do not even want it on my system. I see no advice how to go about removing Impulse and having your games run.
4. No matter what Impulse is a very system hunger program when you are trying to do anything in it and still want to use your computer. I tried Archiving and running a program; the Archive halted but Impulse acted as if all systems were go, and the computer once again ran really slow.
5. Impulse was touted as a simple little program. I have found it just the opposite.
6. Loading a game to run is a very slow and painful process. Games son't just "start" up you wait for them to start through Impulse.
7. Archiving takes forever. Why is this, if the game is already on your system; since it took forever to install and verify?
EDIT: One last thing. I would love to have the games on the drive and in the folder where I put all my games but it takes so long with Impulse it is not worth the hassle to do so, now that I know you have to push the big blue button.
This in itself is reason enough to cast away Impulse. If you do not want to reinstall because of the long time ti takes to do anything, the program becomes useless.

It's like in an adventure game, where you have to melt the wax to make a key to unlock the door to the dungeon and talk to the dungeon keeper and ask him fashion tips so you can wear the right hat when you go to the dance later that night to impress the woman so you can sleep with her, and while she's dazed and confused after some amazing coitus, if you tell your character to use the toilet you'll get flushed down the toilet with your waste and end up finally escaping that prison encampment you were in.
I mean, no one tells you to click on the orb. how in the world are you supposed to know you have to click on a blue orb?! it makes no sense either, why can't you just install the games like normal? or at least use an installer that's clear like GOG's..

Up Up Down Down Left Right Left Right B A
Turn in your geek card. :P
To get back on topic, though, Impulse definitely is on the sluggish side, and I personally don't care much for buying games that are tied to any third party software or online verification systems; I basically view such purchases as akin to rentals. That said, I did end up purchasing Titan Quest this weekend, simply because it was cheap enough that the price was worth it for a rental, and I don't foresee myself playing the game more than once (just wanted a mindless hack-and-slash for times when I didn't want to have to think too much). To put things in perspective $4 is what I spend on coffee each day, so in that light $4 for a game that I hope to get maybe 10 hours of casual gaming out of isn't bad at all. It's all about evaluating what you want out of a purchase, and if the product and asking price match up with that.
As for the complaints other than sluggishness others have already spoken to those, and although I'll agree that the GUI can be non-intuitive at times, that should be a complaint about the GUI itself, not about a lack of options (as those options are there, even if they can be tough to find at times).

Meh, I never played contra, but I think it delivers the point succintly

i too fell for the $3.99 dark crusade weekend deal and installed impulse as a result.
whilst i didnt find the download speeds bad at all, i havent been able to actually install the game yet because everytime its downloaded (4gig download, now downloaded 4 times!) it just says invalid download and/or gives a 404 not found error on the EULA.
the worst thing about it is that if you get the invalid message you have to download it all again. it doesnt store it anywhere even though the program is supposed to have a temporary directory.
i aint alone either. it seems invalid downloads, resulting in taking hours to download again, is a common problem.
i wont be buying anything else from impulse. tis crappo! pfft.

From my experience Impulse only creates start menu icons. I personally like this as I hate having my desktop cluttered with shortcuts, and for those who do like desktop shortcuts copying the start menu shortcut to the desktop is pretty damn trivial.
This one I actually had to look up. It basically archives the game in its current version so that if you want reinstall the game you can do so without having to re-download it.
Impulse can be removed via the Control Panel (Add/Remove Programs). As far as I can tell games will still run fine if Impulse is removed (might be different for different games though).
Start them through the start menu, not through Impulse.
Archiving involves compressing and copying several gigabytes of game data. This naturally requires a bit of CPU overhead and takes a while.

You can set that in your Preferences (the blue orb).
DarkPhoenix pretty much covered the rest.
Again, I'm not going to argue the intuitiveness of it. I agree it's not intuitive. For what it's worth, I'm also not a fan of third party software required to play games. The only reason I have Steam is to play Mass Effect. I was not a fan of the Steam concept originally and only finally broke down to get Mass Effect without SecuROM and its activation limits. But I hate Steam and won't be buying anything else through it. I find Mass Effect starts up slow as hell because of having to wait for the bloody Steam client (whether you're on-line or playing in off-line mode).
I'm not even a fan of Impulse. It's just another Steam-like app, IMO. But at least I don't have to fire it up to play the games I bought through it. The only reason I have it on my system is because I bought Sins of a Solar Empire and Gal Civ 2 last spring and then this fall it was announced that further patches will only be available through Impulse. Since I already have it on my rig, I figured I may as well figure it out. The options ARE there, but sometimes they're not, as you noted, easily found. Anyway I now view it much like DarkPhoenix: I'll use it to grab something like Titan Quest that appears as a cheap deal. Since it's only 4 bucks, I figured I'd buy it. But I won't be using it to buy new games.

the red pill or the blue pill?
XD

I am starting to think only gog has the pill with no after effects. I do not think I will be fooled again.
Now, where is my Stardock Super Secret Special Blue Orb Decoder Ring?
Ah, I think it is this button marked Uninstall!

Was impulse the DD service that prevented modification (mods, uofficial patches etc.) of game files or was it some other service?

Perhaps one day there will be a digital download project which will allow me to:
1. Buy games.
2. Download them as many times and whenever I want to.
3. Install and play them without having to put up with any additional software and DRM crap.
Until then I'm using GOG for old games and retail for new ones.
EDIT: Yeah, spelling..

Unfortunately these days more often than not you end up being tied to some/all of the crap youd end up with if you bought the game from DD instead. (IE retail game can have (more likely than not) DRM, be tied to Steam or Windows Live etc.)

True. But there are some publishers that don't use DRM. The latest example can be Ubisoft and their little 'experiment' to publish Prince of Persia without DRM. I wonder how that went and what is their stand today...

That WAS Steam previously...I've heard it's grown easier for modders to work their magic on Steam editions these days, though.