That it goes to 3 levels rather than just 2 is great news, and will get me itching to buy a copy as an "intro to D&D" set I can eg take on vacation when visiting my in-laws - my brother-in-law likes the occasional D&D game. 
JohnSnow:
"Just as an aside: 4th-level is a very easy jump from 3rd in 4e. You get 1 feat, +1 to 2 stats, and +1 to skill/ability checks/attacks and defenses. That's a pretty easy advancement for a DM to allow, or even for WotC to slip in (1 line in one table)."
That's a great point, and it would be nice if WoTC included that line in the set to allow people to transitionally level-up to 4th while the GM went hunting for the full rules.
I agree that 5th level would need a bunch more pages and might be impractical, but they could include that line for 4th without adding in extra monsters and magic items; the GM can run a session or two with the level 1-3 stuff, just more of it.
At 3 sessions to level, that would give around 10-11 sessions or ca 40-50 hours of gaming in the box, without needing to start over at 1st, which compares well to most video games.

JohnSnow:
"Just as an aside: 4th-level is a very easy jump from 3rd in 4e. You get 1 feat, +1 to 2 stats, and +1 to skill/ability checks/attacks and defenses. That's a pretty easy advancement for a DM to allow, or even for WotC to slip in (1 line in one table)."
That's a great point, and it would be nice if WoTC included that line in the set to allow people to transitionally level-up to 4th while the GM went hunting for the full rules.

At 3 sessions to level, that would give around 10-11 sessions or ca 40-50 hours of gaming in the box, without needing to start over at 1st, which compares well to most video games.