It's shit.
I'm so glad we moved forums - no way could I express my opinion on this bag of wank with a swear filter in the way.
Let's take an example shall we:
I'm trying to convert a 3.5 Dragonborn Cleric / PrC Pally into a 4e Paladin who multiclasses as a Warlord. That should make sense right? Not too much of a stretch of the character concept?
So, I spend 1 feat and get a skill and Inspiring Word 1/day - well whoop de fucking do! But that's not the bad bit; in order for multiclassing to be worth the feat slots the powers you swap for have to be better than the ones you're getting rid of, right? Well, the best Warlord powers are the ones with extra effects keyed off of your Inspiring/Tactical Presence choice, but since there's absolutely no fucking way of getting that class ability when you multiclass, the Warlord powers you can choose from are thoroughly underwhelming choices!
Oh, and remember, this is when I'm trying to build a Paladin/Warlord. I can't afford a decent Wis, coz the MAD of the Cleric and Paladin is a fucking joke, so most of the Paladin powers are pretty shit from where I'm standing, but despite that the Warlord powers I could swap them for are shit as well!
Which fuckstick designed this crap?
At least in 3.5 you could multiclass and dip to salvage a poor class - no chance now! It's like wotc thought the multiclassing was causing the imbalance, when in actual fact the multiclassing was caused by their own inability to write a class worth sticking with!
I'm ending up thinking my 3.5 Dragonborn Paladin is better served by converting to a Fighter, because the class doesn't suck as much as the Paladin. But to be a Dragonborn Fighter is shooting yourself in the foot - you don't need the Cha boost, and the Fighter can cut minons to ribbons without needing a breath weapon. In fact, if you're anything other than a Dwarf as a Fighter you're shooting yourself in the foot! Getting rid of the flexibility in the system won't solve the "problem" of optimization, it'll just drastically reduce the number of optimal character set ups and force people to play the same old characters over and over and over!
AAAAAAAAAAARRRRRRRRRRRRRRRRGGGGGGGHHHHHHHH!!!!!!!!!!!
The one multiclass feat that might be worth it imo is the Paladin one - since Divine Challenge lasts until you use it on someone else, having it 1/encounter isn't such a problem - use it to mark a solo/elite is all. Other than that, spending 1 feat for a Paragon path you like might be a good deal, I can't see multiclassing being much use beyond that.
Come back 3.5! All is forgiven!