This might have been the top game on my list if it wasn't for the horrible check-point save system.
Well, the developer has released a patch since then that has fixed most of it. All except for the save system. This is how it works: the game gets saved whenever you approach a special pole with a green light on top. These poles are strategically placed around each map so you won't have to spend a lot of time running around looking for one (although, it does sometimes happen). Here's the part that really annoys me: if you happen to be in the middle of a mission and exit, you're placed in the beginning next time you launch the game thus loosing all mission progress. What gets saved is loot and XP's. Perhaps this kind of weird checkpoint system IS acceptable for handicapped consoles (I believe that is the politically-correct term nowadays). For PC's, this seems like a huge step backwards.
Another annoying thing is rapidly-respawning bad guys. Some missions make you to traverse your way back when you suddenly realize you have to fight the SAME enemies you wiped out just a few minutes ago. In many cases it's just not worth to waste your time and ammo on them: they don't give any special loot and all the ammo and weapon chests are already empty, credit to your previous passage through the area. I'd just run through hoping by the time I get spotted I'd be far enough not to get killed (see the paragraph above for explanations on what happens if you get killed mid-mission).
Overall, the game is fun. There's a huge list of main and side missions, but the majority can be described as such: find and press/pull a few button/levers, find some parts for some weapon weapon, kill X number of Y. Each subset of main missions is culminated with a boss fight. After a short while the game becomes very predictable... except for the loot.
There's TONS of stuff to loot. I'd estimate nearly half the time you spend in game is looting and comparing your current arsenal to the new weapon you just picked up. If you're one of them packrats who likes snooping around for the next best thing, you'll feel right at home. Each newly found gun promises to give you a killer upgrade, but gotta be careful though, a seemingly powerful gun may have a drawback that would make you hate yourself for selling your favorite one for this replacement.
I also enjoy the cartoonish atmosphere thanks to the comic-book-like graphics. It makes blowing somebody's brains out a whole lot less disturbing :) Telling the truth, I really don't care about the whole in-game violence issue.
Oh yeah, if you enjoyed the game, make sure to try the Zombie Island DLC, you won't regret it, I promise. On the other hand, don't get the Moxxi Underdome, it's just a huge arena with waves and wave of bad guys for you just to mow down -- this is as creative as it gets.