Yay Harlan!
Jams together I Have No Mouth & I Must Scream, Deathbird Stories, and Shatterday into one massive package, with the usual addition of profound, inflammatory, funny and enlightening forewords, prefaces, introductions, and similar ephemera from HE.
Good stuff here, although I Have No Mouth. . . comes off as a much weaker collection than it actually is, since two of its strongest stories were cut as duplicative of the 'story cycle' in Deathbird. Certainly the right choice, as an editorial matter, and Harlan makes it right by giving us some extra stories and essays in their place, but worth noting.
I'd say it'd be a good place to start getting into Ellison, except for the fact that it was a book club item that's been out of print for 35 years (and, oddly, has a TON of typos, which I'm sure pissed Harlan off) and so costs substantially more than it would to just acquire each of the three collections individually.