how is it?

Interesting! I played a lot of SS13 years and years ago, mostly on /tg/station. I saw the trailer for SS14 during the PC gaming show a few months ago. It brings back a lot of memories for me with the rough edges sanded off. I don't know what SS13 is like today so it's hard for me to do a direct comparison between the two.

more user friendly?

I have no idea how SS13 plays today, but SS14 feels a lot more modern than what I remember. It's off that god-awful BYOND platform and running off of a custom engine called Robust Toolbox (heh) written in C#. The performance is generally lag-free and can handle some wild player counts (Colonial Marines is capped at 350 people and has ~160 in a game right now late on a Sunday). It also allows for neat stuff like piloting shuttles in game. For example, when you play cargo, you actually have to fly the cargo shuttle to the trading station. You can also build custom shuttles (lovingly called shittles) which salvage has to do. There are a lot of context menus when you're constructing/deconstructing objects that tell you what tool you need to use next so you aren't left guessing. Perhaps most interesting to me is that the movement isn't grid-based, it's all free movement so you don't get in those weird juggling-back-and-forth-with-another-character situations.

expanded mechanics?

Quite the opposite on the official SS14 servers, at least. Plenty of things are lacking, particularly in medical. Currently, there is no surgery, genetics, or virology on the official servers though surgery is a focus currently. It's also lacking in antags as well. You're limited to traitors, thieves, nukies, zombies, and rarely rev.