I've had occasion over the past week to do some work at the walk with all my horses. The footing in our indoor arena was replaced last week, and it's still too deep for my taste - it's like walking on a beach above the high tide line. No work above the walk for us in that footing. We have been able to manage some rides in the outdoor arena - it has a sand track around the outside which I rarely use - but a nice grassy area in the middle that's firm footing. Since all four of my horses are barefoot, firm footing is just fine - they've got good, shock-absorbing feet - their frogs and heels absorb the concussion instead of their hoof walls (shod horses) transmitting concussion up the leg. Too soft footing, however, is an invitation for soft tissue injuries. The footing in the indoor will settle down in a bit, and we're mostly riding outside except when there's rain or mud between the barn and the outdoor.
The walk is so fundamental, and is so neglected. Everybody is in a hurry to trot and canter, but trust me, if it's not working just right at the walk, it won't be any better at the trot and canter and is likely to be worse. If you haven't got a good walk, you've got nothing. There is also so much to be done at the walk - so much that is beneficial to the horse and builds a foundation for later work.
Have you got automatic forward, no nagging, from the first step?
Have you got straightness?
Is your horse soft and engaged with almost a zero pressure in your hand?
Have you got bend in both directions, with the inside hind stepping under?
Can you do walk/halt/walk transitions without bracing or abruptness?
If you ask for back from halt, is the response a brace or soft, relaxed backing?
Can you get lengthening/shortening at the walk, with appropriate changes in posture and stride length?
And you can add other things, for fun - spiral in/out and lateral work.
I've been having a lot of fun at the walk, and all the horses have really been excelling.