G1 varies wildly in quality. The animation isn't all that great in the series itself as it was bottom the barrel even for the 80's (Hasbro was putting their money to driving Transformers and G.I. Joe into the ground and funded MLP and Friends with whatever money they found under the sofa cushions.) I judge the episodes more on the writing. Going by that...
The first two specials are good with the very first special being unapologetically awesome. The characters of the first special were also developed by the people being the Dungeons and Dragons cartoon, and I really wish they had used that style all the way through.
The movie suffers from massive pacing issues and an unwillingness to be about anything. It's got some funny scenes and is as watchable as any other movie Hasbro made at the time. The animation started going downhill here which is a shame since the style was beautiful. However, ponies in the wrong places was rampant and they never bothered to finish the Twinkle Eye ponies' eyes.
As for the series itself.
I would watch the episodes written by Michael Reaves (The Return of Tambelon, The Magic Coins, The Quest of the Princess Ponies, Flight to Cloud Castle) as well as Crunch the Rock Dog by Linda Woolverton. They're the series at its best. You can also watch the episodes written by David Wise (The Revolt of Paradise Estate, The Magic Door, and the episode starring the Big Brother Ponies no one remembers the actual name of) if you to see some really weird crap.