First of all, the internal components of Gaggia Classic, Baby, Evolution, Carezza, Espresso, and Coffee are identical in terms of espresso brewing and steaming. So read this as a review of all of those.
This is my first real espresso machine, and with it I discovered real espresso. Gaggia has a well-deserved reputation as a great entry level machine. It has drawbacks, but what do you expect for $200?
I drink mainly straight double shots, so I'm sensitive to flaws in my espresso. As I have grown more consistent in my technique, this machine has started to hold me back. The little boiler simply can't provide adequate temperature stability. If I start a double shot right at the end of a boiler cycle (when it's at its hottest), the boiler will be cycling again by the time the shot is done. So, every shot of espresso sees water from perhaps the entire "deadband" temperature range (and maybe a little cooler).
To compensate for this, I try to choose forgiving blends. Darker roasts with "bottom-heavy" profiles are best; I've had good luck with Paradise Roasters' "Espresso Nuevo." I find I get the best flavor if I start my pull maybe 10 seconds after the boiler cycle ends (that is, after the light goes on). Ristrettos are usually smoother - presumeably because less cold water is flowing into the boiler.
Now that I've ragged on the machine, I have to mention: I make consistently better espresso at home than any of the 5 independent coffee shops in my town. Some of them fancy themselves gourmet, too... ahh, to be a coffee snob...
I recently rigged a brew pressure gauge, and found that the machine was producing 14 bar at the group, which is about 50% more than the ideal. The problem was a seized up expansion valve which was easily poked free due to it's shape. Now it's down to 9-10 bar, and the espresso I'm making now is heavenly. A lot of the harsh flavors I had been attributing to brew temperature were actually because of the immensely high pressure.
The gaggia sucks at steaming, but with some technique and tweaks it can do alright on small volumes of milk. Here are the problems and some tips for overcoming them:
1) Small Boiler = Not a lot of steam
If you just hit the steam button, wait fot the light to come on, and start steaming, you will have a lot of steam- for a few seconds. The steam volume quickly dwindles, however, to a trickle. The reason for this is that the element is off. In order to get good, steady steam, let the machine get up to temperature, and then wait for the brew light to go off, indicating that the heating element is on. Wait four or five seconds, and start steaming. Unfortunately, the element is so powerful that the machine sometimes "catches up," even when the steam valve is open all the way. To compensate, you might hit the brew button for a split second to pump some cool water in there... or else you can do what I do, and just drink straight espresso.
Also, don't steam in anything more than a 12-oz pitcher. That's enough for one latte or two cappuccinos.
2) Turbofrother = junk
If you want nice froth, you gotta lose the sleeve on the turbofrother, leaving you with a simple, single-hole steam tip. Unfortunately, that bare tip is a silly little short, stubby thing which can't reach very far into even a small pitcher. The motion of the ocean is all well and good, but let's face it, size matters. Luckily, Saeco's "Panarello" wand is compatible, and the has an inch or two on Gaggia's. You can buy one for $10, and it's totally worth it.
A note on grinders:
I started off using a Capresso Infinity grinder with this machine. The grind quality was fine, but it only had 20 steps, which didn't provide fine enough adjustment to really dial my shots. I eventually bought an Innova (Ascaso) i2, which kicks some serious butt. I'd consider the Infinity to be a "bare minimum" grinder for the Gaggia Evo, but I'd recommend something at least on par with the solis maestro plus (in terms of adjustibility).
Edited for grammar; added content 2/27/07