Pros: Highly transparent, resolving, detailed. Very quiet. Compact. Pairs well with almost any set of headphones.
Cons: Not cheap. Doesn't quite play at the same level as more expensive TOTL amps
Addendum, May 2015: Since writing this review in late 2013, I purchased two other headphone amps, both considerably more expensive than the L-2. One of these amps is the Apex Teton. It deserves 5 stars for sound quality, as it is hands down the best amp I have ever heard. The other amp is the Eddie Current 445, which deserves 4.5 stars. Both the Teton and the 445 are better sounding amps than the ECP Audio L-2. The transitive property means the L-2 deserves less than 5 stars, my original rating. 4 stars seems about right to me. The L-2 is a great sounding amp that beats a lot of the competition, it is a bargain if found used, and I think it is worth its original sales price. But, yes, $5,000 amps sound better than the L-2.
I have owned the ECP Audio L-2 for about 2 months now. I also own an Eddie Current Super 7 with NOS tubes, including Tung Sol BGRP driver tube. I have previously owned the Woo WA22, the Luxman P-1u, the DNA Sonett, and the Singlepower Extreme Platinum.
I can honestly say that of all the amps I have owned, I only really liked three right out of the box: the Super 7, the Singlepower Extreme, and the ECP L-2. That already puts the L-2 in rarified company, since my first impressions ended up being lasting ones and led me to eventually sell the WA22, the Luxman P-1u, and the DNA Sonett after trying but failing to like them.
The Singlepower Extreme will always be close to my heart for its warm sound signature. But it had horrible build quality and ultimately failed. The ECP L-2 has stellar build quality in comparison.
So, what do I like about the L-2? Here my short list of two prized attributes:
(1) It has all the positive musical attributes of a good tube amp -- it is slightly warm and full-sounding, not at all dry or boring. Although Doug Savitsky of ECP Audio is a no-nonsense builder, this amp is not a "straight wire with gain". It is really immersive and musical. I also don't find it to be at all bright, as Skylab found. I am sensitive to bright, fatiguing sound. I only could only listen to Grados for about 15 minutes before I needed to take some Advil and return them. The L-2 is good for hours of fatigue-free listening. The amount of mid-range and treble detail this amp offers is also really impressive.
(2) It has none of the negative attributes of tubes -- it is extremely quiet and barely gets warm. I really like using my JH16s with full-size headphone amps. The JH16s offer sound quality that rivals the best dynamic open headphones I have owned or demo'd, but they also isolate really well. The one drawback of IEM's is that they are highly sensitive with very low impedance. If there is any noise in the circuit or from the tubes, you will hear it with the JH16s. When I use the JH16s with the L-2, I hear absolutely zero noise. This amp is as quiet as the solid state Luxman P-1u. Also, unlike some tube amps, the L-2 is not a space heater. You won't risk burning your children or pet with this amp.
Comparing the L-2 to the Super 7: the Super 7 is a great amp, but in my book it gets edged out by the L-2 in every respect except one. The L-2 is quieter and offers slightly better resolution and detail than the Super 7. The Super 7 sounds a tiny bit rolled off in comparison to the L-2. The L-2 also seems to drive my LCD-2s better than the Super 7 does -- offering better dynamics than the Super 7. The L-2 also has significantly lower gain than the Super 7, allowing me to use much more of the volume pot than the Super 7 does (a particularly nice feature with the JH16s). The only aspect of the Super 7 that beats out the L-2 is in the area of bass quantity and depth. Simply put, the Super 7 has really authoritative bass, easily the best of any amp I have owned. Bass-shy CDs tend to sound better through the Super 7 than on the L-2. Overall, I am finding that I am listening to the L-2 about 80% of the time, switching back to the Super 7 20% of the time.
Yes, the L-2 is an expensive amp. But so are the WA22 and the Luxman P-1u, neither of which compete with the L-2. The Super 7 is a cheaper amp, although when you figure in the cost of finding NOS tubes for it, the spread between the cost of the two amps falls quite a bit. Although I have no intention of parting with either amp, if forced to I would sell the Super 7 before the L-2.
Summing up: it's a shame that ECP Audio is somewhat overlooked as an amp manufacturer on Head-Fi. My guess is that this is a result of ECP Audio's (i.e. Doug Savitsky's) approach to marketing, which is to completely avoid it as far as I can tell. He does not frequent this forum very much, let alone attend a lot of meets. As a result, there is not a lot of buzz around his amps. I have owned a lot of high profile amps in the last 7 years and the L-2, in my opinion, easily competes or beats all of them in terms of sound and build quality.