I decided to splurge and get the Tracer bundle (the simple one with just her and the Specter skin.) I've only played one game with her so far, but she's got a very interesting feel to her.
Tracer is, of course, the flagship hero of Overwatch, and is all about speed, mobility, and time-bendy powers. She is going to be absolutely terrifying in the hands of a skilled player, but to play her to her fullest potential, you'll need to be able to manage her movement in clever ways.
Tracer's biggest advantage is that she gets to auto-attack on the move. You'll be dealing way more damage through your auto-attacks thanks to this, but the price you pay is that she only has 20 rounds in her clip. Hitting D or simply emptying her guns will reload, which takes very little time, but it does mean that your attacks will be interrupted occasionally.
She's also pretty fragile, but you have a lot of tools to escape enemies (and hunt down retreating ones.)
You get three charges of Blink that will recharge over time. This lets you teleport a medium distance very quickly, which will be really great for chasing down fleeing enemies. It's also, of course, a pretty handy escape tool (though another ability fills this role more clearly.)
When within melee range of an enemy, you can hit W to do a quick burst of damage to them. There's a talent that can make this an AoE ability, which is quite nice.
Hit this button to rewind time, going back to the location you were a few seconds ago. At level 20 you can upgrade this to also heal you back to your previous amount of health, which is pretty great. This has a long cooldown than the others, so use it judiciously.
R: Pulse Bomb
Tracer only has the one heroic ability, but she gets it at level 1. This will shoot an explosive a relatively short distance from you (it's a skill-shot) that will then explode after a couple seconds and slow down affected enemies. You'll need to charge up this skill by using your other attacks, with various talents affecting the way your abilities recharge it.
Tracer is a lot of fun so far, and her ability to fire while moving is very powerful. I played Garden of Terror, and not only could I fire on large groups of enemy heroes trying to catch me as I retreated, but I was also able to dodge around the big garden terrors during the night phase without letting him get too many hits in.
My main recommendation is to save Recall for desperate situations and use Blink to chase down fleeing foes. I might update this as I have more insights.