Since you haven't played the old school originals, there isn't much point comparing them to the new XCOM for you to judge the new game.
But the new XCOM is absolutely awesome, probably the best tactical game since...Silent Storm? The difficulty is brutal even for veterans, for newcomers you can expect 50% KIA each mission on normal difficulty for your first few hours. But the game is absolutely fair, and beating game on Ironman/Impossible is a damn proud of a badge you can wear everywhere.
I'm a oldschool player who have played X-COM, TFTD and Apoc, the new XCOM is streamlined that's for sure, but it's also more fair, less random, and better balanced as a tactical squad game. The expansion pack introduced tons of fun equipment and toys to play with, but also has several deadly, brutal, merciless missions that destroy hardcore veterans if they're not prepared for them. Newbies probably won't survive at all.