And here I disagree. There are some people who just want to be able to say "I hit it". The focus in Essentials of everything a Martial character does being some form of basic attack really simplifies matters. And the Essentials characters don't track who's marked/cursed/quarried/etc as class features.
Just how dumb do you think these players are?
You know, two years ago there were thousands upon thousands of new players who learned how to use at-wills, marking, curses, quarries, etc. etc. with little to no problem.
Yes, Essentials in comparison to Classic might be "easier", but that doesn't mean that Classic is "hard". Fact is... BOTH are exceedingly easy to play if you have someone who knows the game and knows how to explain rules to people.
Unnecessary. This isn't a three-year campaign he's putting together... he's putting together (from what it sounds like) a one-off or two-off game so that his players can see if they might like 4E. So worrying about crap like class balance, errata is not worth your time getting into, because as DracoSuave said... these players won't know the difference.
But either paperback is cheaper than the hardback. Monster Vault vs MM1 at low levels is no contest at all (and at high levels MM1 monsters simply don't cut it so although MV has fewer epic monsters it really isn't missing much - and has no Dracoliches, Purple Worms, Needlefang Drake Swarms, or Wraiths*).
Again... if he's buying books in preparation for a long-term game... then perhaps going straight to all the Essentials might make sense. But he's apparently not. He's teaching them the game. Why go through all that money to buy all these books if there's no guarantee he's ever going to use it again? So there's absolutely no reason to buy the Monster Manual *OR* the Monster Vault at this point in time.
And as for five classes vs eight, cancel the Warlock - that thing is not for newbies. The wizard in the PHB has some serious problems - not so in Essentials. And I'm not sure that the pre Divine Power Paladin works well enough either. Plus the Heroes books don't read like computer instruction manuals.
You are coming at all these problems as someone who's been playing the game this entire time and can actually COMPARE things to each other. The PH Warlock most certainly CAN be for newbies... as there were thousands of people who did that very thing when the first PH got released. The wizard
doesn't have serious problems unless you put him right up against an Invoker and start going over the two classes against each other with a fine-toothed comb, and the Paladin also works "fine". ESPECIALLY for a bunch of players who can't compare these classes against anything else.
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Sure, if the OP is intending on spending $75 to $100 on D&D books just to have, even if his players decide NOT to keep playing... then sure, buying the Essentials line isn't a bad way to do it.
But if he's looking at the easiest way to get what he needs to run a simple game and doesn't want to buy a whole bunch of unnecessary stuff that might not ever get used again... since he already HAS the DMG... picking up the first PH and running Kobold Hall or the free Keep On The Shadowfell is the easiest way to go. And hell... he could probably not even not bother buying the PH and just download the six pre-gen 1st level characters off the Wizards site that they released when KotS was first put up there.
Download KotS and the six pre-gens from the Wizards site and voila! You can teach players how to play D&D without spending ANY money whatsoever.