I have to agree though the only noticable mistake is the black lines on the boat and the casino guys. I can tell you got lazy by the obvious shadow copying and pasting. One of the shadows is overlapping the lamppost.
The people on the street and the cars look sexcellent, but the piece is very unfinished. Either halfway through you decided to raise the standard, or halfway through you got lazy. The guys in front of the casino look completely different from the rest of the people, better fix that. Get rid of those nasty black lines as well and this will be a favorite.
Lose all the black lines (replace outer ones with darker colours of the inside colours, and inner ones with lighter colours of the inside colours) and this will look quite good.
People have shadows, cars have shadows, phone booths have shadows, wtf there are no shadows included with houses, some posts, trees? This is a real turnoff! It is unfinished work, better finish it.
Number one lesson in pixel graphics. Never use crappy compression, it makes you lose that lovely pixel crispness.
In whole, this looks kind of half-done. You've used black outlines on some elements and dumped them on others, making those with no outline look kinda flat and the ones with them out of context.
There's a lot of lovely detail involved, but the picture lacs a distinct style and crisp colors - something a piece as massive as this most certainly needs.
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Hey! You got some really nice things!