In order for a bar to keep from fading into obscurity in the drinker's paradise that is New York City it has to have something, anything that sets it apart from the crowd. Maybe the chairs are more comfortable than normal, maybe the bartenders are exceedingly, well, tender or maybe it has the best jukebox for blocks, but there needs to be some kind of edge.
Grassroots' edge is popcorn. An old glass-fronted popcorn popper sits at the end of the bar, enticing weary travelers to partake. The smell of butter and salt perpetually fills the air and the mad scramble towards the bar when a new batch is being prepared has to be seen to be believed.
Apart from that (and the fact the drinks are slightly cheaper than average for the neighborhood) there isn't really much to tell. Located on St. Mark's between Second and Third Avenues, Grassroots is a wonderful place to hang out on a Monday or Tuesday night, and an accident waiting to happen on the weekends when all the local NYU students come out to play. Their selection of both beer and hard liquor is impressive. There are a good number of tables to be commandeered, most of which are vaguely separated from the bar proper by a chest-high railing, an appreciated feature come the weekends. There are TVs by the bar that are too conspicuously placed for my tastes, but the bar staff are friendly enough to, if not turn the damn things off, at least distract you for a bit.
If you ARE going to go, make sure you go early, snag a table, ruthlessly defend it. You might want to bring some friends as well - their pitchers are one of their better deals.