RE: How to get back into playing?
I only recently began playing, so I do not have any experience with the ex, DP, and HGSS sets. But from what I've seen, most seem to agree that today's modified format is faster, and far more centered on Basic Pokemon (the new EX cards, primarily). This isn't a bad thing, in my opinion, but there are those who object to it.
If you are at all interested in playing the game again, I would have to say that you should at least give it a shot. No matter what I or others tell you, the only way to find out for sure if it's worthwhile is to go at it yourself.
How should you do this? Well I started by playing a deck on an online simulator (specifically PlayTCG, as it does not cost anything to use and gives you access to all modified-legal cards with no other restrictions, but the official simulator, Pokemon Trading Card Game Online/PTCGO is a lot more streamlined, graphically and mechanically, while having a cost to play anything but the provided theme decks).
If you would rather get right into real, physical play, then I would start by going to a close-by league. There, you will be allowed to bring cards outside the legal sets (so your old ex and DP cards are still allowed), although I would encourage you inform your opponent that you are not using a modified deck prior to play, just as a courtesy. If you find yourself interested, you can start to build up your deck with better cards. Alternatively, you can build a modified deck from scratch. If you find yourself leaning towards the latter, I would very much so advise checking out the
Deck Garage forum for some ideas. You can also test decks in a simulator before building them for real.
Oh, and you should definitely go to any pre-release events as they occur. It's a great way to play for fun while also getting your hands on new, modified-legal cards. The next prerelease (as I am typing this) is for Furious Fists, which will take place on the weekends of August 2-3 and 9-10.
Have fun!