You know I've been thinking to myself as to why I've been so negative about essentials in many ways. Although my opinion has changed from not buying it at all to buying it out of curiosity and as some stuff like the mage sounds cool, I find that what really gets to me is the MM1.
All the "Players" books have been updated or won't be made irrelevant by essentials, but what about the original Monster Manual? Writing
this thread the other day made me realize just how far behind that book actually is now. We have no indication that anything in there will ever be adjusted or errata'ed, I can appreciate though that would be an enormous amount of monsters.
Unfortunately, many of the monster manual creatures are fundamentally broken. Wallowing in immense pits of mediocrity and requiring considerable altering of powers and damage just to be made viable with what is the "norm" with post-MM3 creatures these days. What is getting to me - increasingly - as a DM is the concept that the Monster Vault that revisits numerous older monsters (IIRC) is basically paid for errata. I love new monsters and pretty new stat blocks any day, but I can't shake this feeling the monster vault is basically just going to make the original MM irrelevant. Bear in mind unlike other "My books are going to be uselessss" whines, this I feel is strongly supported:
MM1 creatures are way behind on maths - damage, defenses and attacks.
They are way behind on power design - Many of them have a simple melee basic attack and nothing else.
It has the most worthless minions ever - big changes to minions were made between MM1 and MM2!
It has very few viable solos in the book, who work anywhere near as well as recent ones and they are even more severely behind in maths. There is a reason half the threads for killing a solo monster with a single character focus on Orcus - he's a total chump (the empowered Orcus from E3 is better though...)
I mean if any book gets entirely replaced by essentials and the monster vault, it will be the Monster Manual.
Ironically while I will complain about that on one hand, I must state that I indeed hope the Monster Vault does precisely this as well. It's pretty clear we're not going to get updates to old monsters to new damage/power expectations and similar. So I hope the monster vault "replaces" a lot of older broken creatures like the Pit Fiend (who is just terrible), gives us viable chromatic dragons (Some need more help than others, eg White Dragons) and such forth. The things from MM1 that have been firmly left too far behind to use without major modifications.
It do concede that of all the books published in 4E, the original MM is the last book I look at for monsters now. While I know that for many things, I will still be looking at my PHB and original DMG even post-essentials.