I agree with roqua, the Altar UFOs are decent games, and Afterlight is probably the best one yet.
That said, there's much to improve. The maps get awfully repetitive after a while and some of the map designs are just idiotic. Firstly, why the hell does my away team start their assault from the bottom of a steep hill on some maps? They arrive by a goddamn aerial transport. Even more stupid is that you start OUTSIDE your own base when defending it. What the heck?
The combat engine is among the best I've seen in the RTWP department. Using a combination of slo-mo and pause you could probably make very intricate tactical combinations and maneuvers, the problem is you don't really have to. Through most of the game (On hard difficulty, and I'm pretty sure the actual AI don't get any better at Very Hard) the only "tactic" I had to use was concentrating my firepower. Stupid AI is not unique to this game, but one should expect more from a tactical squad game anno 2007 than a game 10 years older, RT or not nonwithstanding. This is probably my main complaint.
Another flaw lies in the weapon balance and some of the more stupid character development design decisions. If you choose in a certain way in a certain situation your squad gets a killer weapon doing 999 damage or something like that, while at the same time being extremely long ranged and accurate. This in itself is pretty stupid, there are few things I hate more than EXTREME über weapons. To add to this, one of your main sources of experience is damage done in combat, which means that this weapon is even more fucked from a balance perspective. Sure, it has only 10 shots per engagement, but still. Another dissappointment is when you research sniper rifles. Despite having their own specializations that take a few valuable days from one of your grunts to learn, they are generally fucking weak compared to most weapons.
Personell management is pretty well done on the other hand. Since you have a very limited pool of people, there are a lot of hard decisions to make. There are Techs, Scientists and Soldiers. There are also characters combining any of the two professions. Techs are used for production, base construction and out of base construction. Scientists are used for research and land surveying. People being both soldiers and one of the other professions can also play a role in some combat missions. To add to this there are a lot of further specialisations in each of professions, these take valuable time to learn. All in all, it's one of the ups in the game.
If Altar continues to improve on the series (AI is the first and foremost concern) I think they could make a truely great game some day. As it stands it's worth playing, but you might tire of the repetetiveness before you complete it.