Banana, nothing wrong with Marin Trail, sure things have move on a little with trail building in the last few years but it’s still a great ride.
Plus what’s wrong with a bit of fire road now and again? It gives you a chance for a breather and an oppertunity to appreciate the views before you nail the next singetrack section. That longish downhill on fire road is where you can get some serious speed up so it’s still excellent fun.
Also from the Marin train you can link into some excellent natural (and cheeky) riding across to Llyn Crafnant and Trefriw if you have an OS map handy.
Hate the way people bash some of the older trail centres these days. That’s pretty much akin to kicking your grandparents up the arse because they now walk a little slower than they used to.