Congrats on your Mesa Express purchase!
I bought the Express 5:25 1x10 last summer and have been really happy with it. I wasn't initially shopping for a Mesa, but the Express won out after much comparison with Vox, Traynor, Fender and Marshall tube amps.
It is perfect for me because I wanted a high-quality, versatile amp -- my musical tastes are very diverse, ranging from strumming/finger picking on the clean channel, Brit invasion stuff with the crunch channel at low gain, and classic rock and 80s metal on the crunch channel, blues channel or burn channel. It may not be enough for those who want a "modern" metal tone, but it has plenty of gain for my applications.
I do most of my playing at my home or at jams with friends -- its small size and portability are ideal for this use, especially when I get the chance to crank it using the Class A 5W setting.
I occasionally lust after an extension cab, but, since most of the time I want good tones at a lower volume the 1x10 is fine for now.