This game was not a disappointment. But certain parts of the game, definitely were.
I am, what i like to call a "trophy whore." I start playing a game, and within a few hours of starting, i get bored. However I continue to play, because i like to have a lot of trophies. On Modern Warfare 2, i got bored about the time you go through the airport killing people, but i continued to play, and ended up beating the game, just because i wanted the trophies. But anyway, on Borderlands, I was never bored with the main story line, although since I'm a trophy whore I wanted to do every mission in the game so i could get more trophies, which i did by the way.
The fighting system was very fluid, and had very few problems. One problem i must mention though, is when in vehicles, your turret and or rocket launcher, have very limited mobility to where they can shoot, which makes certain parts of the game rather difficult.
Driving cars on this game is very hard at first, but the more you get used to it, the easier it becomes, by the end of the game, i hardly left my vehicle when possible, because it became so much simpler to just run things over and shoot them with my rocket launcher than to actually shoot them with my guns (plus this way i didn't waste as much ammo).
The whole weapon system was great. You very frequently found guns that were better than the ones you were using five minutes before, and that makes the game a lot of fun, because when you first find a new gun you think "Oh my god, this weapon is amazing" and then you find a gun that does five more damage, and you proceed to use it instead.
I was the Hunter character, Mordecai, and he was a lot of fun to use. In most games i like to either use a sniper rifle and be back away from the action, or right up in combat with an SMG or machine gun in hand. However I was able to do both on this game. With my snipers doing as much damage as they did, it became easy to just use it as a shotgun when i got into close range. (I had a level 19 proficiency level when i beat the game because i had killed so many people with it).
Boss battles are far too easy and are not at all difficult (for the most part). Sledge (the first main boss) presents the biggest challenge in the entire game. He has a huge shield and has a freaking huge sledge hammer type thing. In addition to him, you also have dozens of little midget psychos, several normal and/or burning psychos, and quite a few bandits. in a very small room. This makes the battle with Sledge quite difficult.
Other than Sledge all of the Boss battles are anti-climactic and somewhat simple. When playing as the Hunter anyway. I'm going to guess that they would be harder with the other classes. In the fight against Krom, you enter this valley with him on a turret that shoots rockets, and has a machine gun. However As the hunter, I stood behind a big rock, shot him 3 times with my sniper (from about 500 yards away) and his turret blew up, killing him. (Although I have to give credit to my gun, it did 343 base damage, plus it had x4 explosive damage, so when i shot, i frequently did well over 2000 damage).
As for the final boss battle of the game (I'm not going to spoil the ending or tell you about the boss), I stood far enough back, that he didn't even realize I was there, so I just shot him with that same sniper over and over again in his critical hit spot, and he died. I didn't even get hurt.
These types of boss battles were very very anti-climactic and very disappointing to me, as i was hoping for a challenge. But despite the bosses being easy, the actual creatures you fight throughout the game, are sometimes very difficult. You know what I'm talking about if you've played the game, when you're a level 15, and then a level 18 bad ass fire skag comes out, when you're trying to kill that and 2 dozen other enemies at one time. Things like that, are pretty hard.
Overall, this game presents a good, fun challenge that will give you many many hours of satisfying game-play. If you liked games like Fallout 3, but you also love first-person shooters like Halo or the Resistance series, you will love this game, as it seamlessly mixes RPG leveling and depth of game-play with the action and intense combat of FPS's.