Valkyria Chronicles is definitely the most similar thing I've played to the new XCOM, but I feel that XCOM is a lot better balanced of an experience.
I liked Valkyria a lot, but I ended up cheezing the whole thing by using mostly scouts and running up on troops and shooting point blank from the back. If I didn't do that, I'd never be able to finish the level quick enough to get a high mission rating. Their rating does not reward careful tactical play. It just wants you to be fast.
Not getting a high mission rating meant you wouldn't get enough experience to level up your troops and keep pace with the story missions. Since you can't replay missions, you'd be forced to grind out the same boring training missions over and over. Fun game, but the experience system is way flawed.
Final Fantasy Tactics is my other go-to tactical game, especially with the difficulty mod that makes the game a lot deeper and more balanced. It doesn't feel all that similar to XCOM, but managing troops, getting better gear, chess-like movement and all that. It has a bit more in common with old X-com, but still it's a classic.