daniel7345: Simon 4 is alright, his voice will annoy you a lot though - Simon now has an irritating american voice. The graphics are nice, though, and it's point and click again. It's not terrible but not as fun as the first two games.
Simon 3D... the graphics are horrid, but if you like the humor, jokes, and story of the first two - try Simon 3D.
I haven't been able to buy Simon 5 anywhere, so I can't try that to say if it's any good.
They used to sell English version of Simon 5 in Gamersgate, but then the German company which made the game went bankrupt and it seems that they have stopped selling it. There's also a disc version available, but unfortunately it's in German.