Ok, finished it too. Thoroughly enjoyed it but I can see why some TOTC fans might be disappointed.
In my opinion TOTC was really about San Fransisco, multiple linked storylines, huge cast of characters with only the city as its unifying theme. This time it's Michael's story (he isn't really Mouse any more) and it's told from his pov hence lots of characters "missing" and it's a much more straightforward narrative.
It's also a novel about getting older, being settled, realising that there's way more behind you than stuff to come so it's fairly melancholy in parts and less "sparky" for want of a better word.
There is a lot of reminiscing and each character is re-introduced with a couple of pages of back-story which I did find a bit irritating. I suppose it's there for those who didn't read the previous books (although it wouldn't work as a stand alone novel imo), or perhaps acknowledging that it's been a long time and people might need a reminder. Doesn't do anything to move the story along though. I seem to recall that he did tend to do similar, though briefer, summaries in the other books though.
If you're a huge TOTC fan then it depends on whether the stories were so important to you that you want the characters to remain as they are, frozen in time. I think he's done a great job of bringing the stories up to date but they are living the lives of 50/60/80-somethings now and it's a very different world. Some people might prefer to let things be but I always want to know what happened next.
There was one bit very near to the end that did bring a tear to my eye and all in all it was great comfort reading. Well worth getting out of the library or in paperback.