Not totally sure what someone who never played the original X-COM series would think of this, but as an older gamer who played that back in the day, I can say that this game truly captures a lot of the same tactical fun and isometric turn based combat. And for the most part it does it better.
I have the original X-COM on Steam, but it is so old that the sound and graphics are VERY dated and the resolution limits how much you can see so that you have to pan around the map a lot. But in this game, you can play at 1920x1080 resolution, resulting in being able to see a lot more of the map which is very satisfying. The music and sound effects are good and appropriate for this style of game.
There is a lot less granular level of control over your "inventory", you don't get to sell/buy most things (grenades, flares, ammo, missiles, alien scavenged resources) as you do in the original x-com, you just spend money on making or buying important resources like people, ship and weapon upgrades mostly. This can result in you having less changes to pull money out of your stuff to sell, so you have to be very careful with your budget. That is the one negative in my mind, I kind of liked being able to sell off a lot of recovered stuff if I was short on money, however there is an advantage here as you only need one store room per base. You can sell a few things, but often not enough to get a lot of money, relatively speaking.
The ground combat is awesome, and even the air combat is a lot improved over the original, you can "auto resolve" it or you can actually try to outsmart the craft and get behind them for better results sometimes.
One massively convenient feature is the fact it auto-equips your soldiers with unlimited flares on night missions. I really sucked in the original series to go out on a night mission without flares, you were as good as dead usually!
Lastly, I would recommend playing the "Community Edition" which you can get from the "betas" section I believe. It actually has a lot of improvements and bug fixes over the last official release.