All games could be better than what they wind up being. Deadlines, limitations of current hardware, glitches, human mistakes, unforseen conflicts with hardware and other software (mainly a problem in PC games), poor ports from other platforms, budgets that run out of money, committes of idiot executives that force changes but don't know anything about making good games etc. all combine to make even the greatest games less than what they could have been. That said, I do have a list of a few games that were so horrible I can't see why they got published but they should have been at least descent:
Enter the Matrix - I know movie games have a poor track record in general but come on! How could it have gotten this bad? I saw games five years older than that one made with smaller budgets that looked and played ten times better. Non-round tires on cars? Character models with gaps in the skins? They couldn't even manage to rip off Max Payne's bullet time right and it was a major part of the Matrix movies.
Braveheart - Should have been the greatest sword swinging epic game ever but it was a poor dud that wasn't even as good as Baldur's Gate.
Tomb Raider series - How has this series survived this long? Even the first game's Lara was so hard to control that I could barely make her do basic platforming moves let alone the tough ones. They have yet to improve the gameplay significantly despite all the graphical tweaking. Sure L.C. looks cute but I'd rather look at pictures of a hot real life girl dressed up as Lara than struggle though a Tomb Raider game. The god-aweful Angelina Jolie movies "based" on the games didn't help any either.
Batman games - How can they continue to screw up games based on the coolest super hero? Batman should be a lead pipe cinch to make a great action game from. If they can make such good stealth and gadget laden games for made up for the game characters like Solid Snake and the hero of Deus Ex, why can't they do the same for the Dark Knight Detective that so many game characters are inspired by?