I played it for a few on 360, and its....I dunno. It was okay. I got bored of it after a few hours and sent it back. The character creation is kind of cool. Crackdown is still my favorite game of that genre lol. Vs GTA 4, GTA4 is definitely a better made game. I dunno about pure fun factor though.

I have Saints Row II on Steam (from the THQ Complete Pack) and Mercenaries 2 on retail and I have to say, Merc 2 is awesome. It's a little broken in some areas but it's a great time and the blowing things up parts are great. I hate how there's QTEs in there but it's good. Have not tried Saint's Row II yet but I imagine it's a smaller scale but more detailed brother to GTA IV.
Another game I imagine you will probably like is The Saboteur. Like Mercenaries 2 (same developer, in fact) but set in WWII Paris and you're part of the French resistance.

Have you tried The Saboteur yet? It got my interest, but there's so little hype about it.
Hmmm so GTA4 wins Saints eh...maybe I'll look into Merc 2. I need a good mindless freeform game.

If you do try out Merc 2, watch your ass, literally.

All three of those games you mentioned, Saboteur, Saint's Row II, and Mercs II, are all buggy messes. Saboteur is the most fun of the three, because it feels like they were actually trying to achieve something. Saint's Row II was one of the worst open-world games I've ever played.

The Saboteur's only broken when you use an ATI card. I use a nVidia card and I seem to have no problems.

So would you suggest getting Merc 2? I see that I can get it for £9.99 or so from GamersGate UK vs the £60 or so price tag on the EA Japan store...

I'm not just talking about the PC version here. I have had some crazy bugs pop up on me, like falling through the ground and finishing a long mission without the mission ever ending, on the PS3 version. Also, the game was kind of rushed out the door, and that's visible by the screens and screens of text you have to go through to get mechanics explained to you when they come into play.

There is so many levels of wrong there.
I say get it, if you can tolerate messes here and there.

It can't surely be worse than Saints Row 2 could it? I mean, I can't even drive a single car in SR2 with out the frame rate suddenly dropping to 5 fps. And that's on a fairly high end system!

Saints Row 2, if it isn't unplayable on your system, is amazing and I would recommend it to everyone.
Mercenaries 2 is okay, but I wouldn't say it adds anything to the table. The original Mercenaries is FAR better... but it isn't on the PC. If they ported it I would buy it immediately. It might be worth $5 if you really like free-roaming games.
Saboteur was awesome - I didn't have any issues (bug-wise) with it at all. It was also a very enjoyable game with a surprisingly atmospheric final level.

Not in the perfomance sense, rather in broken gameplay. QTEs and all that.

As a mindless blow everything up action fest mercs 2 is good despite the many bugs and poor AI. I got close to 20 hours of gameplay out of it without feeling bored or that I'd been grinding out the same missions, basically just did the main storys and hit some of the extra targets on the way to them, even missed out the pirate faction completely.
The main thing about it is if you can see it it can be destroyed with enough firepower, cars, trees, houses, skyscrappers. QTE are annoying as anything though, going to break your spacebar trying to hijack some of the super heavy tanks in the game.

I payed $10 for Mercenaries 2 a while ago and had fun with it. It's good to play every now and then, but I do die a lot. Although I also died a lot in the first one, but that's probably cause I'm doing something wrong.