Lets see what I can remember.
To start with, none of the latest games were, imho, as good as the original two with terror from the deep being rated in my books just a TINY amount better than ufo - both were awesome. I really didnt like apocolypse much though, it was okay, my friend LOVED it to bits, but I just kept playing xcom tftd again and again. I also dont think aftermath managed to fill the shoes of its predecessor completly. Still something.. not quite right. But for all I know im suffering from fanboi syndrome and not thinking things are as good as tftd simply because they ARNT tftd xD So in the end you will want to draw your own opinion - i expect demo's exist
Anyway, Aftermath WAS a good game despite what I say about it not being as good as tftd. I enjoyed playing it, the research trees were there in full (obviously researching the laz weapons from ufo and not the sonic ones from tftd - another thing i prefered from terror was the sonic weapons and aquatic everything xD). Now, I may be not remembering this right.. but I really cant recall any of the base building. I cant remember a damned thing about it. I have this feeling it wasnt there. You placed bases and you used them, you could research upgrades i think.. but I really cannot remember placing a single building in my base like you would in ufo or terror. I will have to replay it to double check that though, but if i cant remember anything about it then its pretty safe to assume it was disapointing.
In game was classic xcom though! I was playing turn based (not sure if you can switch like you can in apocolypse, but i always prefered turn based anyway) and it was still about getting the right guys with the right weapons to the right place and scouring that unexplored area of the map for the last alien praying to God he haddnt already spotted you and had a gun aimed at your favourite vertens head. Yes the characters still develop - as far as i remember you can still give them names you like, they get better as they become more experianced and you dont want them to die.
I dunno if i got as engrossed as I did with terror though, I recall having a special squad, all named and hand picked and maxed up to the highest ranks and if any of them died I wouldnt be able to bare it and reloaded - I dont recall quite the same sense of urgency in aftermath but it was there in some form and again this could just be tftd fanboy syndrome talking
Havnt played the new one yet, im going to make sure I do.
and now i fancy starting up terror, except its quater to 7 in the morning and i havnt even slept yet, thankyou very much