Concerns
1. Players need better feedback on whether the Judge has received their action
2. Effects need to be explained better so Players know how to use them
3. I wish I could move the Chat and Log windows to the side instead of on the bottom, so more of the map is visible on my widescreen monitor
Prep
Yes, better prep would have helped. Apparently Players can create their own characters if they start their client in Judge mode. When they're done, they can then restart their client in Player mode and they can "Upload Creature".
Visuals
The map and tokens are only going to look as good as we can either make or find online. When creating maps, a more definitive difference between Wall and Floor needs to be used. Maybe next map I'll go old-school black (or grey) lines on white. Or something like that.
That being said, I found a Dundjinni User Art Pack last night that has hundreds of high-quality free tokens in them to use.
Voice Chat
Yes, voice chat would probably be nice. Once we get used to the app there'll be less program-related 'splainin' to do. I really liked that Melbosa threw in the in-character comments, that was cool.
Play Style
I noticed that at first no one knew how to proceed; everyone was waiting for me to move the tokens, while I was waiting for someone to say, "My character walks in". It was nice to see that we got past that fairly quickly. The intent of the tool is to let the Players tell the Judge what they want to do, and at times to just go and do it, but that it's very much still the "My character does this / My character does that" play style that is used around a table. In other words, it's not a video game with a human opponent, it's still pen-n-paper style D&D.
System-Specific Tools
d20Pro has more tools to help the game progress than the other Virtual Tabletops I tried. The other ones all focus more on being system-independent. Things like declaring an attack, or a skill check, or anything like that either have to be done through a chat window and a third-party die roller or by spending a bunch of time programming macros. While some (like MapTools) have really pretty mapping and per-character fog-of-war, I found d20Pro's system-specific tools to be surprisingly helpful last night.
As Lazy said, though, having a little more stuff prepped (especially Effects) would certainly help.
Summary
I found our test-run mostly satisfying. If I were given a choice of no D&D or D&D with d20Pro as the Virtual Tabletop, I'd pick the latter.
Question
While we were focusing on the mechanics of this tool, did you notice a bit of plot or story coming out? I did, between the narratives and the in-character comments and even one of the monsters surviving long enough to say "Arrgghhh", and I liked that. Good to see we weren't completely focused on mechanics, even in a test.