Tzolis is just 20. Has enormous potential, but the reality is when given the chances at Norwich, his performances weren't good enough.
He needs to be managed well, and in hindsight would have been better to go a different league where he could get more playing time, and develop his game. But when PL comes knocking, and the signing fee is lucrative for a 19 y.o., it's a life changing opportunity and you can't say No. Saying that, we don't know what is going behind the scenes, if he's happy or not. Probably not, as he is not getting much opportunity to play with a club that's relegated. I am certain, that Norwich believed they had a gem and that the price they were picking him up for was a bargain.
If you look at Liverpool, they bought Tzimikas for a similar price (I think it was a bit more, 12-13k) and he has been there for nearly 2 years, and while not a regualr starter, getting more game time now, he's defenitely improved, definitely happy and enjoying his time at Liverpool, and I would say his market value has gone up, or is expected to go up over the summer break.