I've been saving this one til I competed the set. Was it worth it? No.
1) Heide Park - Nice place to be, well run and a good selection of rides, many of which are stand outs for what they are. Except Colossos, which is by far the worst, but still worth a few goes.
2) Alton Towers - Should be the best by now, but Wicker Man blew it and I've just grown so tired of the place. The lineup is nice and varied and they have 2 of Merlin's best (Nemesis, Hex), though I never really found anything joyously rerideable here even in its heyday. On quiet days now, I get bored and leave early. On busy days I get pissed off and leave early.
Sure, this may well apply to all of these parks if you went enough times, but I don't feel like I've overdone Alton to be honest. It just never feels worth the effort once you're in it.
3) Thorpe Park - I do genuinely like a lot of the rides here and I'd still want to go regularly just because it's there and fun, but haven't had the motivation any more with latest changes in pricing, passes, operations (and investments).
4) Gardaland - It was nice enough, but the rides leave a lot to be desired.
5) Chessington - Don't like what they've done to the place, can't remember the last time I went and nothing has been done since to make me want to return.
6) Legoland Billund - The standout Legoland with a single noteworthy and unique attraction.
7) The other Legolands - Overpriced and copy paste. Just cred stops to me now that I've since started skipping completely.
Windsor has a certain charm I guess but don't care, got the creds (wait, are they getting a new one?)