I've been very impressed by the monster stat blocks, they're one of my favourite aspects of 4e. I see them as very much an evolution from 3e, particularly MM4 and MM5.
3e mostly got monsters right. I liked how they had the same stats as PCs, such as strength scores. A great improvement on 1e and 2e imo, at last I knew how much gryphons could carry and so forth.
The 4e blocks have retained most of the 3e stats. They've done away with feats, grapple bonus, space/reach (the former could be calculated from size anyway so it was pointless in 3.5) and armor class breakdown. Ref save and touch AC have been conflated, skill list is reduced, special attacks and qualities have their own section.
The presentation is a lot better imo, following on from MM4 and 5. Special abilities are *much* clearer, highlighted in bold text. This may seem minor but I think it's very significant. The special powers are one of the most important features of a monster, so they definitely should 'jump out' at the reader. I've missed lots of abilities using MM1 and 3, but I don't think I ever have using 4 and 5.
4e has broken with tradition in that PHB spells are no longer used for most powers. That's a very good thing. It was always lazy design, and boring too. This makes things much easier for the DM at the table.
You could always create unique, flavorful powers for monsters, from 1e-3e, but 4e has really embraced the idea. Every 4e monster now has at least one interesting ability and often more than that. By dispensing with PHB spell powers, a culture of creativity in monster design is encouraged.
In one important respect 4e is stricter than 3e. A monster's challenge rating (now expressed as level and xp bonus) implies a specific range of combat numbers whereas 3e played it by ear. The level of challenge presented by a monster is extremely important, the game has to get it right. 3e was loose where it should've been tight.
3e was strict in completely the wrong place. A lot of stats - feats, skills, BAB, saves - were determined by HD and type. But this added nothing of worth to the game. Not only that but other stats - attributes and armor class - which contributed a great deal to a monster's combat effectiveness were unbounded. It must be great to know as a player that the beast with 150 strength that's kicking the crap out of your PC has the right number of skill points for its hit dice.
