I was wondering what M.A.X. 2 did that turns everyone off to that title to this day. Is it general bugginess? Does the AI now suck? Did they break some core game mechanic?

Haven't tried it yet, but reading some reviews on MobyGames indicates that the gameplay mechanics were changed for the worse.
The guy behind MAX wasn't involved with MAX 2, and most people think that's why MAX 2 turned out so bad.

I still own both (original boxes and all). I still have M.A.X. on my hard drive and on every build since I bought it. M.A.X. 2 went on for a few months, then came off and never went back on.

And as far as I remember they did away with the connecting pipe thing, I really liked that novel idea in the first.

MAX 2 is not a bad game at all. The real deal is: it is not as good as MAX 1.
MAX 1 is the strategy-games masterpiece.
And another point to remember: if MAX 2 was exactly the same as MAX 1 everybody would say bad things about it like "It's the same thing!" or "We are payin' for the same game with new maps!".
I like some of the changes on MAX 2 like "no-connectors" or "2 shots for Escorts".
I hate that "power" system. You never get enough material/power.
The AI in MAX2 is weaker too.

I've just Installed both,
I didn't even get as far as the AI in MAX 2 - it's butt-ugly!!!!
Can't stand to look at it one more second!

I agree - presentation in this game is really poor - heck most of the time I can't even tell units from the background for some areas.

I bought M.A.X. when it first came out and have had it on my hard drives ever since - it is a truly great game. My friends used to come over and we'd spend entire weekends playing hot seat games. That said, M.A.X. 2 is terrible. Simply, simply awful. The graphics actually look worse than the original and it's a completely different game.

M.A.X. 2 is a lesson in how not to design a game. I don't fault the devs: Gus Smedstad is one of the good guys. He worked on the original M.A.X., HOMM III & IV, and Children of the Nile, among others. In M.A.X. 2 he was trying to do right by the gaming community and it just didn't work out. M.A.X. 2 tried to be all things to all people and ended up pleasing none.
When the game was being developed, you were able to post design and feature suggestions on the main website. I posted several there myself. Practically all, it seems, of the more reasonable and do-able suggestions ended being incorporated into the game, which in the end just made a mess of things. (There might have been other problems as well behind the scenes, but this is the one that really stuck out at the time.)

Can anyone elaborate more on MAX 2? I'm thinking of getting the MAX games, but $5.99 for MAX 1 alone doesn't really seem to justify. I'd like to find out more about MAX 2 and whether I'm getting my money's worth with it too

I can elaborate a bit...Max 2 is a waste of a game, path finding is nearly nonexistent. You will spend most of your time babysitting your units trying to make sure they go where you ordered them.
The game does have groups but it is the worst implementation of groups I have ever seen. You group select units (it can only handle I think about 9) and do a Ctrl-1 (or whatever number I never got past 2).
Then you simply press the number key to reselect the units. The issue is that there is no press number once to select and twice to jump to the units; as soon as you press the number the camera jumps to that group. It is very frustrating to want to simply tell a group where to go, when the camera jumps across the map to where the units are and you have to manually scroll back to where you wanted to send then in the first place.
Oh, and did I mention you can never be sure they will make it there due to the horrible path finding.
Save your $6.00.
This one more shame on GOG for selling this steaming pile of code as a "Good" Old Game.
It can in no way be defined as good.

Thanks. I was even still thinking of getting MAX as part of the GOG promo, but I think I'll just pass after this.

This is very unfair. Max2 isn't as good as MAX, still it's not that horrible of a game.
Now, MAX alone is definitely worth 6$ (how many new games are much weaker than MAX in most aspects save graphics? And yet they sell 60$).

I am not so sure it is unfair as I tried to be accurate, but if there is something that I stated that you have more insight into then you can help others out here and post it.
For me the games are uninstalled and will likely never be installed again.

MAX1 is worth the $6 alone. With that in mind, think of MAX2 as a bonus. Does it make the whole package worse if they've included it?