IMXP, the short answer is no, it'll be different. Not worse or better, necessarily, but different.
For one, the "presence" thing isn't as possible. You can't "control a room." Your players could be in their own places, have distracting tabs open, eating or drinking or not wearing pants or...there's nothing in Roll20 that makes you look at someone face-to-face. You can use videochat, but webcams aren't any substitute for your own personal presence.
Also, Roll20, like any digital tabletop, benefits from ample prep time. If you're trying to do it on the fly, you might be spending a lot of time drawing and picking images, which isn't a great way to spend game time, IMO.
The edge that digital tabletops offer you in your D&D playing is that they make scheduling (which is the biggest bugaboo of most groups) a snap. I play my online game on Monday nights, and I wouldn't even try to play an in-person game then - I can just shut my computer down and go into the next room and sleep when the game is over, no commute required.
They aren't generally in and of themselves time-savers. Personally, I find a lot more time is needed in running one because I worry about things that, in an in-person game, I wouldn't sweat (things like maps and visual hand-outs become all the more important without the zeitgeist of other people around you). Some aspects of them can be pretty quick and automated, but Roll20, even though it's more user-friendly than Maptool, can still require a substantial learning curve to get the most out of it when DMing.
If saving time is your issue (vs. something like scheduling or getting a group in different locations together), Roll20 won't be a solution, it's still running a game, and it still needs prep, and it IMXP needs more prep than most in-person games to truly get the most out of it. What it DOES offer you is the most user-friendly digital tabletop, so if you're in the market for a digital tabletop to begin with, Roll20 is probably a solid choice.
This kind of hits the nail on the head for my experience. I run a Roll20 game weekly and I'm a big fan of the service. I even signed up for the $10/month subscription, which I'm happy to pay for.
That being said, I became much happier with the VTT when I stopped trying to "recreate" the in-person experience. I think what [MENTION=16212]wedgeski[/MENTION] is describing, with players rolling real dice at their table and basically just using Roll20 for a zoomed-out map (no tokens, right?) is probably the only way to "keep doing it the same way." And that's because [MENTION=16212]wedgeski[/MENTION] isn't really using Roll20 with an in-person style. He's using Skype. Roll20 is just there as a convenient way to share a map. At least if I understood his post right.
Sessions where I tried to set things up in a way where I could do them "the way I always do them at the table," usually felt very awkward and unengaging. On the other hand, sessions where I embraced the strengths of Roll20 could work really well. The ultimate lesson that I've learned with Roll20 is: drawing battlemats at a table sucks. Being able to quickly throw up a map that everybody can see is awesome. And they can be any kind of maps. You can take snapshots of your hand-drawn graph paper maps with your phone and upload them, especially if you turn the built-in-grid off so you don't have to agonize over getting your squares to line up perfectly. (That's been a big lesson for me — I keep grids on the map because they help the players keep a sense of scale as they zoom in and out, but I always turn off the in-game grid once I get the scale about right.) You can spend some time drawing maps with lots of textures in photoshop, or you can get a cheap set of "dungeon tiles" and quickly assemble dungeons that way. And, of course, the internet is your oyster. If you're willing to start with a map that somebody else has made, you can find tons of maps on the internet, both for free and to purchase. If you load enough of these in, you now have several general purpose small dungeons, outbuildings, taverns, abandoned wizard's towers, etc, all at your fingertips. And they look cool and evocative.
Some other things worth taking advantage of — load your prep right onto your map. The system provides a "GM layer" for things that only the GM can see. You can use this for labels, monsters hidden under the bed, trap doors, etc. I also put a little "question mark" logo in every room where I would otherwise put a map key. So I'll have a token that says, "15. Magen Vats." Now, if I double click on this token, I get a screen where I can enter "gm notes." So instead of thumbing back between my printed notes and my keyed map and my players pretty faces, I can see where they are located, and I can pull up information about the room they are about to enter without taking my eyes off the map. I'll put room descriptions, DCs on various object interactions (unlocking chests, lifting portcullises, etc), and really anything else that I would otherwise scribble in my notes. The downside — I have to be at the Roll20 interface to type this stuff in, but I can always copy and paste from an Evernote notebook that I use for doing session prep while on the train.
Another tool I resisted for a long time was the dynamic lighting. This allows the game to control sightlines for each character, and it has rudimentary ways for tracking darkvision, light sources, etc. Too much like a video game! I said. But throwing some simple dynamic lighting guides onto another-wise lousy map does tons to elevate the visual immersion of a setting, and it makes the game much more compelling than whatever you're doing on your cellphone. There's a really satisfying sense of discovery as players open a door, see an orc in the center of the room, and then charge in, only to realize that 15 other orcs were hiding up against the wall.
In the same vein, it's very easy to quickly blow up a token on everybody's screen. An awesome monster drawing pulled off of google images can be really fun to quickly zoom in on.
Ultimately, it's all about learning that you have very different ways of conveying and storing information at a VTT than at a real tabletop. The "bandwidth" afforded to your voice and actions is much, much more limited, so you have to take advantage of the communication tools offered you by the actual visual tabletop.
The prep time, I think, is much more than tabletop, but as you get your system down and build up your library of spare maps, monster tokens, evocative artwork, etc, you'll find it goes a little bit faster. If this is ok because you can spread that prep time out into free time that wouldn't work for actual face-to-face gaming, that's great, but I'd say that my prep time went up more than the hour I'd save in commuting to, say, a gaming store. On the other hand, I can start my game at 9pm at night and run it until 1am in the morning. That's why it's worth it to me.
