I gave them a watch over a couple of weekends for the first time in a few years;
Generations - I found had aged at least visually very well, mainly due to the excellent cinematography and good effects, the film only really falls apart at the end for me.
First Contact - always been a favorite of mine, and while it's still very entertaining, somewhat surprisingly it had dated probably the worst of the bunch, the sets and effects were not really a big enough step up from the TV series, but like I said loads of good bits and still very entertaining.
Insurrection - Suffers from a lot of the cheap-feeling problems that FC does but with a dull premise, irritating, preachy characters and no better but still really average effects - TV standard. It still had it's merits, with some decent character interaction and some nice location shooting but the whole thing came across as a bit 'meh'
Nemesis - Strange one this - again, suffers from a lot of the previous movies faults, and it had a silly, cliched, derivative plot, some really dumb scenes with a preposterous villain, but I found it to be easily as entertaining as First Contact maybe even more. I find myself watching the Scimitar battle on YouTube as much as any scene from any of the movies, JJ Trek included, and despite Data's death, find it has a certain charm, with excellent visual effects, and the best score of all four TNG movies.
I'll probably visit them again in a couple of years, I would say I watch the TOS movies more, but not by much.