I'm from Poland and I'm watching our domestic league regularly so I can say a few more words about him. Legia paid ~ 500k euros for him to some Slovakian club and already then media were saying that Legia is doing a great deal snapping one of the biggest (if not the biggest, actually) Slovakian prospects. He started his career in Poland pretty well, at first he was praised mainly for his great ability to find himself in scoring position, he scored a few goals but in every single match (he was even playing as a striker for some time, however it's not his favourite positon) had many goalscoring opportunities and in this case his comparisons with Hamsik find the truth. Then he also proved that despite his young age he's already able to play in a very mature way, he was dropped a little to trequartista role and in the second part of last season and at the beginning of current season - clearly the best trequartista in Polish Ekstraklasa. He has someting special, has that 'smooth moves', dribbling, speed and vision that I, personally, appreciate a lot. When he's in form - he's a joy to watch.
Sadly, in the last few weeks, or even months, he's not in great form and his recent apperances are far from his best, are even far from being decent. I can't remember his last spectacular game that he got used people to. Our local media say that's because he already agreed terms with the new club and he doesn't care more about Legia (even despite a fact that at the moment his club is fighting hard to defend a title ...) and is already looking forward to his new football adventure. Also he had some unfortunate statements in Polish media like 'fuck off People, I didn't drop a from, me and my team are still the best', and people didn't appreciate it, to put it mildly.
In current form he's definitely not worth 8 milions, I wouldn't pay even half of this money for him, but when we look at his potential and his appearances in the past, well, Legia can demand it. I wouldn't say it's a great deal, mainly because the biggest transfer out of Polish league is something like 5 milions, so people here are not used to that transfer fees, but looking only at his skills and big, big potential - it can easily repay in the future.