I can't believe people are STILL griping about wireless being always on. Guys, READ THE BOOK. It specifically says that many secure sites will either disable wireless and only have jackpoints, disable wireless completely (eg for Maglocks) or even paint their buildings with metallic paint that prevents the signal from getting out of the room or building! The 'problem' doesn't exist.
I've played 4E for the last six months or so and our group is having a blast with it. I've got alot of feedback for you, so I'm sorry if this post is a bit long.
My history: I played a little bit of 1e, a lot of 2e and skipped 3e. I thought that 3e went a bit too far on the power scale for the Runners.
1. Yes, Wireless systems are the biggest change. The good news is that they really do integrate the Hacker (what used to be called a Decker) much more into the team. Leaving the Hacker behind while the rest of the team infiltrates the target site is a thing of the past. Now, they can tag along and still access the 'trix for you. Making them even more indispensable is Augmented Reality integration with the rest of the team and securing the team's network against intrusion. Hacking and Rigging is also much more integrated with each other and you'll probably find most of the team dabbling in one or the other, even the magic-users. Everyone should be running encryption, stealth and ECCM programs at the very least.
2. Magic's changed a bit. There are still Magicians and Shamans and alot more besides but their flavor doesn't permiate the game as much as it used to. There's much more of a feeling that magic is 'old news', like computers now don't seem as fantastic as they did back in the 80's, the Shadowrun world's had almost a century to get used to magic being back and it's faced Bug Spirits, Dragon Presidents and Shedim and somehow it's still here. The big problem with 4e magic, my group is discovering, is coping with Astral space. It's not very well described in the book. For example, one of the big points, whether or not mundanes were actually visible to Astral Perception is debateable if you go solely via the core rulebook. It seems to say they are in one paragraph, then they aren't in the next. The good news is that it is a bit more streamlined in use, though you're still going to pay through the nose in Karma.
3. If you love tech, you'll love all the new gadgets, 'ware and guns.
As to what books to buy, I have all of them and I count them all as some of the best purchases I've ever made. Even the fluff is amazing. That being said, while the core book might get you by, I think you'll have a much better play experiece with access to Street Magic, Augmentation and Arsenal. And Unwired when it finally arrives (definitely Unwired, they're promising that it'll iron a few of the bugs out of the matrix, fingers crossed). Beyond that, Emergence is a jaw-droppingly awesome book and probably the best of the fluff books so far (mainly because it also has crunch).
As for the ability caps I don't mind them at all. This isn't a class-based game, there are a great many reasons that you'll want your Runner to diversify even before you hit the cap in your main abilities. Hackers can derive great benefits from picking up Rigging skills. Consider that a Drone is a commlink with legs (or wheels, or wings) and I'm sure you'll see the hacker applications for such a device.
Ok, downsides:
1. Everyone will be rolling alot of dice. You know that problem the Wizard has at level 20 when he casts a fireball? Imagine that, only with EVERY roll anyone makes. Get some trays and a few boxes of d6s.
2. The rules that actually state what you have to roll (eg Logic + Electronic Warfare) are scattered all over the book and are badly organized. Before you start, I recommend making your own summary and organizing it into a folder for your own use.
3. The GM really needs to know and understand how everything works together and the players have to be paying attention and know what their character can do. This isn't easy, the setting is large and complex. The problem is compounded by the badly organized and often confusing wording of the rules (much like DnD). The GM has to walk a tightrope of giving everyone something to do while not letting any one player dominate the session and not killing everyone by mistake. It's all too easy for the Hacker to go off into the Matrix and hog the spotlight, the Mage to go off into the Astral and hog the spotlight or the Rigger to dominate combat by running multiple Drones mounted with Assault Cannons. Using Drones, the Runners can literally field a small army if needed. As GM, you have to consider 3 different dimensions at the same time, 4 if you include AR as separate to VR: Astral, Physical and Virtual. You need to know this so you can counteract the Runner's tricks (such as fielding a small army of Drones). You also need to consider RFID tags and a billion other small details. It's alot of work, particularly since there's only one adventure out and it's a bit... disjointed.
I've found that the game works best as a sandbox. Create a situation, throw in a few surprises, see how the Runners handle themselves in solving it. Make sure their opposition is competant and takes as much caution as realistically possible and be sure to include something for everyone to do. Personally, I've found it a very rewarding experience.
Tip: Seach the 'net for real floor plans and use any visual aids you feel appropriate.