Watched TFAwith several friends (some huge SW nerds, and one casual) and while we had some varying opinions on it ranging from decent if unoriginal reboot to very disappointed, the one unanimous opinion was how bad Finn was as a character.
The character was all over the place, one second tragic child soldier, the next coward, then traitor, then joking around killing his recent former squad mates, then hopeless romantic, and throughout a bumbling fool. "Is this an explosive?", drinking from alien hippo water, not knowing which tool is which, "droid please!", and so on while constantly getting his ass beat.
It was bad. not quite "Jar Jar" bad, but then again I've only seen the film twice so maybe in time lines like "DID YOU SEE THAT!!!!" will become equally grating as "meesa" and his clumsy ball handling defeat of the droid army.
Lucas, to his credit, realised he'd mucked up and severely wrote down JarJar in the sequels, all but removing him from saga. Is it too late to do the same to Finn? We have tons of potential storylines to follow that are exciting: Rey and Luke training in parallel to Kylo and Snoke (we get to see Dark side training!), Poe as hot shot resistance pilot under Leia, etc.
Finn is basically done. The future movies work better if we cut back his role, (writing him out completely sadly is probably not doable) using the convenient coma as an excuse and instead focus on characters that had a more positive response and "worked" better. Heck introduce new characters (maybe a main character East Asian for once in Star Wars would be nice), we have a huge universe.
Persisting with Finn seems to me a mistake that is very avoidable, like say keeping JarJar in AoTC. Let's not do that.