Well, Tactics doesn't have all the base building, research, manufacture etc. And it's playable both in turn based or real time. And it's a little more RPG as in your soldiers level up like in Fallout, you spend skill points and pick perks. But overall I think you won't be disappointed.

Another one to consider would be Jagged Alliance 2.

The UFO games might be something you're looking for. They were made with X-Com in mind. Although combat is real-time with pause.

Jagged Alliance is a good suggestion. If you want a good game with turn-based squad combat, you can't go wrong with Jagged Alliance 2. Much better than Tactics in that regard.

I love the UFO series (by this I mean UFO: Aftermath, Aftershock and Afterlight), but in my opinion they are not the same as X-Com despite the clear inspiration in the old UFO: Enemy Unknown series. I feel they're recommendable on their own merits, but comparing them to X-Com tends to get a lot of angry responses from X-Com fans who go in expecting it to be the same.