I think it will be a case of people loving it or hating it. It will not be a dueling tank, it cant not stand and duke it out, it has to be able to "shoot-n-scoot" or else it will get sent back to the hanger. Count on it.
It will either be a camper's delight (rapid deployment), or a very valuable asset in legit group tank battles where they can make a wide sweeping flaking maneuver and get in position for a side shot. Otherwise, it is simply an M4/76mm with very thin armor if it move to up to a skirmish line. The M3/75's were a pain in the arse for a bit of time after they showed up, but they've backed off quite a bit. The M18, depending on the perk price, could prove to be more of a pain in the arse too until the "new" wears off.
It will be fun to have, I've always said it would add something AH does not currently have: a fast, lightly armored, hard hitting gv. Add in the fact that it is very susceptible to having its turret knocked out by aircraft, it is not going to replace anything. It will be something to be deployed only if a few things are apparent: other gv support, room to use the speed, and minimal enemy aircraft threat. This wont be a "cement hugger" like the Kiing Tiger, etc. 
Like many things in the Main Arena, it has to be deployed in a certain situation same for most Low end eny aircrafts in the LWA. Sure you can up a P40b and fly around, it doesn't mean it will last - however in a typical horde setting it will fly just fine. The M18/M10 would do quite nicely as long as it has air support, close GV support and no I-16s around to disable it.
One thing I do agree is that it would not be a cement hugger. Whether its the M10 or M18, both would be used rather then the typical "lets sit on cement and shoot a few rounds till someone pings us with a 37mm then land".
I am not sure about using an M18 for camping a spawn, paper thin armor even an M8 laughs at, its tough to clamp down a spawn unless you got serious armor like a Panther/Tiger which can dominate a spawn on its own - even an M18 can't break through unless the "camper" is new.
The M18 has its purpose in Aces High, we can argue the attributes it has all night long, someone will still up it regardless for enjoyment and fun as I have been upping the I-16 for the last few days, although horribly slow in the late war arena - I still have fun watching spitfires try to out turn me.
May get 1 kill and die 100 times, but I am having fun as I pay for
