If you liked Silent Assassin, you really should try Blood Money. I too loved SA but BM is the best Hitman game to date. Looking forward for Absolution, it first seemed like some shooter but that E3 walkthrough made it pretty clear it's still the Hitman I like.
I like the hits from Contracts the best, the level design from SA, but Blood Money feels like the most well rounded. Although the clown level was a bit too strange for my tastes.
Blood Money is also the only one that looks great by today's standards. The others haven't aged all that well.
I generally look to mechanics before graphics, now the Hitman series has been pretty consistent with theirs. Basically the same inventory, similar tactics across the games, and crappy AI.