We've been there twice over the past few weeks. It's not perfect, but I'd recommend it, and the staff and owner seem to be trying very hard to do the right things.
It's the sort of restaurant that Waltham needs now (well, at least the people from the surrounding towns who come to Waltham to eat need now). Entrees $14-$28 - your usual new American sort of stuff.
On the first visit, the SO had duck - the required seared breast, leg confit prep. It was quite good with a tasty sauce. I had the short ribs. They were tender, but with really big hunks of fat, which I could deal with, but it was boring in flavor - just kind of beefy. Ana Sortun has nothing to worry about there. We split an app of fried calamari that was tender,but not really crispy enough. I know it's easy to over fry squid and make it tough, but brown and crispy is also important.
The second visit, we were in a little bit of a rush to make a movie, and the staff (well, mostly the owner) was great at getting us out on time. I had the panko-crusted chicken in a pear reduction sauce - very tasty, but again, I wish it was crispier - that's the whole point of panko, right? SO had the kobe beef bacon cheeseburger with fries for $10. I don't know about the Kobe part, but it was an awfully good burger and the skinny fries were crispy. Our only thought was that a different type of roll would be better. The ones they used had a thin durable crust that was hard to bite through and the burger squeezed out when you gripped it while you work ed your teeth through it. They should check out the rolls at Wild Willy's - they're toasted and just right. But a burger and fries at WW will practically set you back $10, so it's a good deal at Tempo, and you get to have a glass of wine and be waited on.
Most table were full on a Thursday night - this place is probably going to be mobbed on weekends once more people discover it's open and check it out.