I think tactically he's actually pretty good, you give him a role and he sticks to it that's why he's been popular with managers like Van Gaal, Mourinho and the national team managers. He doesn't try risky things because he knows his limitations so he will do what he's told to the best of his ability, defensively he has a bad habit of switching off and because of his size he gives away a lot of fouls. Technically he's limited his touch and control are very good but he can't operate at high speed and his passing is limited to being short and physically he's obviously not particularly fast or agile but he is very strong.
I think what you say about Serie A might be correct but not many clubs there can afford his wages and transfer fee, the reports are he's on between £100-120k a week a Utd and I think we've activated an extension clause so he has 2 years to run. Inter & Milan have had new investment and might be able to throw some money around but Inter have alraedy fallen foul of FFP regulations so they probably need to sell before they can buy as they already have restrictions on their squad in Europe. Also, not sure their fans would be happy with Fellaini as a signing for the same reasons we weren't. I can't say I watch loads of Serie A but the game is very tactical and players need to be flexible as managers will often change formation 2 or 3 times in a game but it's a little bit less physically intense than the prem but the technical level is very high.
He obviously wouldn't suit Spain as technically he's not good enough, Germany/France are probably to quick, in terms of style he totally suits the Premier League it's just a case of flogging him to a side like West Ham, West Brom or Stoke who are more his level and would actually be able/happy to play to his strengths.
Turkish league is a reasonably good standard and the attraction for players is they can still earn very good money because of the low taxes plus there's still a chance to play in Europa/Champions League. If there's still money in Russia he'd probably do well there as well.