I played through to the Panzerkliens, they do ruin the game but there is so much goodness beforehand. I really want to pick up the expansion. It's actually hitting the States next month, so I'll buy it.
The game engine is just wonderful. Sniping someone from a third story window and watching them tumble down, bouncing off rubble, is just sublime. There is tons of WW2 era weaponry available, and grenades are more realistic than in any other game.
The story is unfortunately mediocre. Some missions are great, some are not, but it carries itself well because of the combat. Basically if you enjoyed Xcom and Jagged Alliance, this is the ONLY game to capture the same gameplay style. I had some camera issues as well, but patching helped with that.