Honestly I think this game deserves a better rating, if maybe not a near-perfect one.
I found Alcatraz to be very enjoyable - maybe a little short for a complex, serious adventure game. The game's aesthetic is, let's admit it, pretty damn awesome as long as you use the "50's look filter", I understand all the criticism about the flat character textures, but I can't but wonder if it's done on purpose so that granulated sepia filter looks good on them. It didn't take away much from the game as far as I'm concerned.
I think another "problem" (if we could call it so) is the clash between the cartoonish look of the characters and the pretty much completely serious tone of the rest of the game. I wouldn't be surprised if people expected an adventure game full of gags and dumb stuff, only to hit a huge brick wall of expectations. The game DOES HAVE HUMOR but more in an ironic comment, subtle sarcastic joke way. In the humor spectrum it definitely falls under "serious games", though.
I didn't think the characters seemed two-dimensional - although there are many of them and most don't get that much screen time individually, so there's not a whole lot of room for them to be uber complex and introspective. In fact I didn't feel the game was shallow at all (and I had that expectation after reading the reviews) specially when you consider how they treat various adult themes in the context of the 50s: homosexuality, drugs, interracial relations, racism, sex life and experimenting, adultery, corruption, hipocrisy, social justice in a rather backwards era... All around it's a pretty complex and creative game in terms of characterization and human relations, IMHO.
There are a couple different endings and besides the usual "you performed certain actions so you got the good/bad ending" sense, it will affect how the relationship between the main characters develops, which I liked and thought was deep and creative enough to make you feel like you're experiencing a game quite like no other you have ever played. It was refreshing.
This isn't in my top 10 games list and it isn't the most oustanding piece of gaming art ever created, but against all odds (judging by the amount of negative reviews 1954 Alcatraz has) I found this game to be much more enjoyable than I expected, fun and different even if it's true that it fell a little short in some areas and it won't become an all-time classic. I still really recommend you to give it a chance - specially if you catch it on sale - and it might just surprise you.