Actually, hitting the OP directly, I don't think you have to have a character play the same way from 1st to 30th level -- in fact, you can have radically different builds through the tiers (particularly if you loosen up on retraining rules, as LFR does).
Lets take my Deva Avenger -- Isa Sunrise. From first level, she was a pretty typical martyr crit-venger -- weapon prof at first level, RRoT at 2nd, charging around the place and absorbing OAs with Righteous Charge, and relying on her excellent defenses and my prevalence to not get her -too- far away from the group to get her from the day. Her first big shift was around 7th level, as that was around when I had her multiclass into Shaman and take the Avenger power that teleports enemies within 2 of the enemy you hit your Int. Now, instead of running around constantly to try to get her oath on, she had a bit of skill monkey (between the Shaman encounter->daily power speak to spirits and the Deva Memories of a thousand lifetime, she could treat nearly any skill as if it were trained 1/day), a bit of controller (with two attacks that teleported enemies around, she could bunch them up, try to teleport them up to hand out damage and get them prone, etc, not to mention a spirit who could block squares), a bit of healing-leader (as the spirit would hand out some free healing on an OA and she also had a per-encounter heal from the second level multiclass shaman feat), and a lot of striker; she was also deliberately drawing OAs a lot less than she used to as far too many minions handed out grabs, immobolize, or the like on OAs. When she hit paragon levels, I decided I was bored with the old routine of "Oath, Tempus, Charge", saw the changes to Melee Training on the horizon, and I didn't see a good paragon option for an Avenger (Shaman) [there is one, mind. But I didn't see it, and I did see an option I really liked].
So instead I rebuilt her, deciding that she'd focused on some memories of a past life where she was a delver into arcane secrets rather than an initiate into the ways of nature. She changed her alliegence to Ogham (frankly, she'd already lost of lot of the rage that made Tempus a good choice), multiclassing into Artificer, switched her Avenger feature over to Unity [not something you can usually do, but this is LFR, plus when she was built Unity didn't even exist], took a power swap feat to exchange the Avenger lackluster U10 choices for the excellent Artificer Slick Concoction, and took Battle Engineer as her paragon path. Suddenly, she's a very strikery Avenger with a -serious- side of leader, who hands out huge bonuses to hit and damage to most of the party, provides a solid damage boost whenever she's next to her oath target (not to mention a goad to focusing fire), moves her people around to get them into position and teleports out to drag enemies into the party's formation (sometimes multiple times in an encounter, between Crimson Stride, Overwhelming Strike as a basic, the full Unity version of Fury's Advance, and a brooch that lets me recharge Crimson Stride), and in a pinch, can even heal, plus solid nova abilities between the Battle Engineer utility power and action point powers, Painful Oath, the ability to optimize the hell out of the Unity damage feature by moving allies around, and minor action attacks from Fury's Advance and at 17th level, Soulforge Hammering [which also provides a nice damage boost during a nova round].
At 21st level, I expect she'll change again, as I'm going to take the excellent
Soul of the World ED, which will force me to decide which races and classes I'm going to poach stuff from; probably gain a bit more control and a few new racial tricks.