DON'T DO IT!
Or, do do it, that "Don't do it" was really me trying to send a message to my pre-S7 self through you. I think you should definitely see them all at least once. I was lucky enough to have first watched Buffy when I was too young to notice the stuff that now grinds my gears about S7, so when I did my big re-watch last year I probably could have done without S7 and gone away happy, remembering S7 as a good if tinged-with-sadness ending to a great show. Instead I watched it and I regret that so much, not because it's particularly bad, but because it ruined that half-formed memory that I had sort-of treasured.
Some have said you only really dislike it if you over-analyse it or rely too heavily on what you've read beforehand, but personally I watched it with no preconceptions (or certainly no negative ones) and with the fullest intentions of just enjoying the ride, but I couldn't. It just was not enjoyable.
Warning, potential spoilers ahead. Read on at your own peril.
First off, there was the fact that straight away I was presented with the fact that Willow had been in England, on MY side of the Atlantic, and no-one had informed me at the time. (I was like 12 at the that time, so I've no idea what I think I could have done with the information, but still). Then, Willow seems to get over Tara pretty quickly, which is painful for me as I'M not over Tara yet. In fairness, she's later shown to be not as over Tara as it first seemed but then that kind of gets ruined by that bloody potential of hers.
Secondly, Buffy seems off. Of course, Buffy's always a little estranged from the group, what with being the chosen one and then what happens in college and then dying and all, but there seems to be something else that I can't put my finger on. I don't know, maybe I'm just projecting my sadness at the end of Buffy on to Buffy, maybe it's even written in a way that makes you do that, but it just didn't work for me. Also, the boot-camp phase with all the potentials at the house AAAARRRGGGHH!! it's excruciating, particularly the endless speech-making and the brattiness of the potentials. I did, however, find it funny how Andrew comments on the speech-making in "Storyteller" so I guess I can live with it.
Finally, what really gets on my nerves is that the whole thing feels like it's trying to be epic and it sort of fails. The big bad feels like Glory over again to me, with twists but nevertheless, Glory. This doesn't help with the whole "this is the biggest big bad we've ever faced and it might be too strong for us" thing, you just know it's all going to work out in the end. Of course, you always know it's going to work out in the end, but I can't seem to suspend that knowledge enough to let The First really worry me, even though its powers are pretty freaky. Caleb is very good as the big bad's physical presence but probably needed to come in to the equation a lot earlier. The way the bad guys are taken down in the finale is a bit weak, imo. Willow's part in it and the scythe are just wrong. I can't explain why, they just feel wrong.