Obviously since President Obama was doing the picking, almost anyone he appointed to the Supreme Court was going to be very liberal. The main question was just how bad the pick would be. CNN has a factsheet up on Judge Sotomayer, so you can see for yourself.
In my opinion the GOP should not fight this nomination, bad as it is. They can't stop it, unless some damaging information about Sotomayer emerges, and just it isn't worth the effort. Sotomayer is obviously qualified, and she's replacing another liberal justice. Republicans should just grimace and accept that she's going to be on the Supreme Court. The GOP needs to pick fights it has a chance to win.