I first read MS&T when I was a kid, back in the early 90's. And I'm reading it all over again now -- after having read all the SoIaF books published to date. Well, the experience has proven quite the oposite of what I expected. I'm enjoying MS&T even more than I did the first time. Maybe because I expected I would enjoy it LESS; after SoIaF, I thought MS&T would feel a bit juvenile or even childish. It didn't. Actually, this re-reading made me realize that a book can exist within the strict boundaries of a genre (say, High Fantasy) and still be a work of so much craftsmanship that it transcends its very niche... if you know what I mean. MS&T, nowadays, certainly doesnt feel like a revolutionary Fantasy epic, but it is, in my opinion, the best possible epic done strictly within the boundaries of the genre. It is, if you allow a bit of philosophical license, the platonic ideal of a Fantasy epic. And that's why it will always hold my imagination as it first did.
Also, as big a fan of aSoIaF as I am, I have all the traditional complaints about the series: it is getting too long, and too many interesteing characters have died, without being replaced by equally interesting new ones. So, in a way, it is a relief to read a series which, although also very long, has actually come full circle, and one which has (in my opinion) a number of interesting characters up to the end. In a way, it's a curious thing that Martin has followed Williams' step in a good and in a bad way: it has gone further on the daring side of fantasy, which is great, but it has also gone much much further on the wordy side of fantasy, which can be great, but can also be not so great.
So, in my opinion, MS&T is still the great classic of modern High Fantasy.
(Please forgive any grammar mistakes. It's been a while since the last time I wrote in english. Cheers).