Just as an aside, multiclassing seems really disappointing on the surface, but there's some things to keep in mind...
1. You will always be your first class first and your multiclass second. A fighter/wizard is still a fighter, and a wizard/fighter is still a wizard.
2. That said, a power here or there actually does go a long way towards being that other class.
For example, let's say you're level 10. You've got 2 at-wills, 3 encounters, 3 dailies and 3 utilities. If you've taken the 3 multiclass feats, fully a third of your limited powers are from your other class, and having an encounter power from that class means that you're guaranteed to act like that class at least once per encounter. Maybe even twice if your substitute utility is an encounter power.
At level 20, you've got 2 at-wills, 4 encounters, 4 dailies, and 5 utilities. 1 at-will, 2 encounters, 2 dailies, and 2 utilities are from your multiclass. In other words, almost half of your powers are from your second class.
So multiclassing, though it seems limited on the surface, really is very close to being half/half. Of course, you still only have the abilities of your primary class, so probably closer to 60/40.
There are a few downsides to multiclassing, though. First, it costs feats. You're spending feats on new options, but you've got the same overall number of powers. Second, paragon-level multiclassing means not getting a paragon path or its associated features.
Of course, multiclassing also allows you to take a paragon path from your multiclass, which might be a more attractive option. Then you're not sacrificing any features.