Why You Shouldn't
Hardcore Trek continuity freaks may have difficulty accepting that Khan and Chekov recognize each other, as the original episode with Khan aired the season before Chekov joined the show. But really, if that's the most you can quibble about, you need to get out of the house more.
Impact on the Franchise
Spock dies! For an entire movie, even! Plus, the consequences of Kirk' legendary cocksmanship among the many fine green-skinned ladies of the galaxy finally rear their ugly head here, with the appearance of a heretofore-unknown son (the ensuing paternity suit should have been the plot of the sequel).
A bare-chested, mulleted Ricardo Montalban chomps his way through the scenery in just about every scene he's in, either quoting Moby Dick and Shakespeare or just staring longingly into a viewscreen while saying "Kirrrrrk..." Also look for a young, hot, pre-Fat Actress Kirstie Alley as Spock' protÃ©gÃ© Saavik.