Agents of SHIELD (AoS) is linked to the Marvel movies, but the episodes only reference random characters or events, the episodes are mostly independent from the movies.

The series takes a while to find its feet and I don't recall ever really liking the first season. Seasons 2 & 3 are where it develops its characters and builds up bigger seasonal story arcs. Seasons 4 & 5 are a little mixed, we even get an appearance from a high-tier Marvel cinematic character (reimagined for AoS). While season 5 definitely promised a lot, with our Agents literally tasked with saving the world, however it fell a little flat. Season 6 was quite fun, largely because of Enoch and some nicely woven together story arcs. It was the first to have a reduced episode count.

In my opinion, AoS is more fun and action packed than the newer Disney series that are padded with mundanity, however you can tell when Disney's influence impacts on AoS story writing and it becomes most apparent in Season 7.

Season 7 is a time travel arc. It's not necessarily a bad thing to use time-travel to make a social commentary on the differences in historic culture compared with today. While in the past, characters are often confronted with the social issues of that time. It is a little cliche now though, and when over done, can come off a bit cringe-worthy. What saves season 7 from being a rip-off of Legends of Tomorrow are some nice touches like the time-period themed opening titles and a film noir black and white episode.

Overall criticisms are that lives mean nothing when some characters can be easily "resurrected" while others are killed at random and barely mourned. It does undermine a death scene when there's a good chance a character will be brought back again in some form. Visual effects are quite good for TV and the writing is generally quite good, at least some thought is put into creating a new story arc for each season.