It did quite genuinely get me to not buy the game and just get The Alters instead at the time I was considering it. Fantastic game, absolutely worth the cost of not buying Hitman.

That guide is out of date, I think. It's simpler now, and almost like a normal game.

This image is linked on the Steam Store page, annoyingly hidden below the 007 First Light advert, and lists which levels are included in which edition.

The Standard Edition, that's on sale right now, includes the modern (base game) Hitman 1-3 levels, plus some Hitman 1 DLC stuff (like Patient Zero campaign). The Deluxe Edition, that's not on sale, adds some DLC levels and missions. Special missions with Eminem or the new one with Snoop Dogg are separate DLC. Standard Edition + Deluxe Pack DLC would get you the Deluxe Edition for like 50% off, although you could just get the Deluxe upgrade later down the line of course.

Something I always found shitty is, that you can't upgrade from Hitman Part 1 to the Standard Edition, without essentially buying the levels again.