In play, the swordmage is great. I imagine you probably want to hear a few more details that that, though.
It might be easier to follow along with this if you take a look at his 3rd-level character sheet.
He typically rushes up into combat with a charge. Eventually, that is; he’s got one of the lowest Initiative scores in the party, so there’s a good chance the warlord or the rogue (or both) will already be in the thick of things. He’s got a splendid basic melee attack, so his charges deal damage more often than not.
While he’s up there, I’ll mark one of my ally’s opponents, if possible. If I have the choice, I’ll mark whoever the rogue is fighting.
The subsequent rounds of combat really depend on the situation. If the rogue has gotten smacked and I’ve teleported over into flanking, I’ll probably stay right there until we crush the target — probably using Greenflame Blade for the damage, but possibly using Lightning Lure if the enemy has decided to try to run away.
If somehow we’re not flanking anyone, I might try to shift over into a better position, again using Lightning Lure to pull an enemy over if it’s worthwhile.
The marked enemy getting crushed within the flanked space has a tricky choice. He could try to attack me, but I’ve got impressive AC and I’m not really dumping that much damage into him. Or he could try to attack the rogue, who has a lower AC and is churning out a frightful amount of damage. But if he hits the rogue, then I teleport over (sometimes a square or two to maintain flanking, sometimes just remaining in the same square) and beat on him. It’s very effective.
Transposing Lunge is also a fine attack to get keep an enemy into a flanked situation. Occasionally I’ll use it just for the damage and not teleport the target anywhere.
Every once in a while I find myself surrounded, or against a swarm, and it’s time for Sword Burst. Or some enemy breaks out of combat and tries to run off, and it’s time to change my Dynamic bastard sword into a javelin and throw it into his back.
Of course, every once in a while the wizard gets into trouble, or the rogue (actually, he gets into trouble a lot more often than that.) In those situations, Dimensional Warp has saved our bacon. I’ll usually be the one warping in, but in theory it could be the warlord. It’s always handy.
Frost Backlash doesn’t get a lot of use, of course, as a daily, but when it comes out, it gets the job done. Half damage on miss is a nice touch.
The other players and their characters are also learning how to orchestrate with the swordmage. The rogue knows that if he’s in combat, his buddy is coming over to flank. I would estimate about half of the rogue’s attacks in an average encounter benefit from combat advantage. He also knows that if combat gets too hot, his buddy will teleport him out of there.
The warlord knows that there’s someone with a worthwhile basic attack to give an extra one to. He knows Wolf Pack Tactics will help me get into flanking. Heck, I’ve seen him stroll past a marked enemy, hoping he gets tagged by an opportunity attack so that I can use Aegis of Assault. That’s some good teamwork.
The wizard is also working with the team, dropping in the ranged support. If melee threatens, I can offer a teleport.
In 4E, the game isn’t quite so much about individual character optimisation and what you can accomplish. It’s more about party optimisation, and what the party can accomplish. It’s a good change.