Disclaimer: I don't want to alienate anyone who has never played a game of past gens. Don't let any of the other questions asked prevent you from asking something that doesn't seem as important. The answers in this post require some requisite knowledge to fully understand. Please do ask questions about the most basic of things in addition to any advanced questions you may have. Those questions are easy to answer so why not try?
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Q: What does modern DPP look like?
A: From a broad look, it's a lot more diverse from what you remember in the LatiMence days. Those threats centralized the metagame into using them and/or beating them with having a method to close a game. With their ban, a whole host of Pokemon are much more viable. Dragonite, for example, which was completely niche in those days is now a prominent threat. Grass-type like Shaymin, Breloom, Roserade, and Venusaur are able to run a variety of sets since there isn't an automatic check to them found on every team. The same goes for Fighting-types like Infernape, Machamp and others as being very potent. The emphasis on speed tiers is a little different. You're able to be more selective with where you cap certain things.
Q: Is there a dominant team archetype or style?
A: Bulky offense is prolific right now and with good reason. The most defining threats like Jirachi, Tyranitar, Zapdos, Dragonite, Heatran, etc. are really good at taking advantage of their coverage and move pool diversity. You can give those standards surprises, in addition to pairing them up with more interesting options like Bronzong, Clefable, Venusaur, and many others. In fact, there is so much diversity that the old standard stall team is not as reliable as it used to be in the LatiMence era. Stall can still be effective, but the approach is different from just selecting hazard setter, pseudo-hazer, and support. It requires more inspired choices because the threats you will be facing are not as limited as they once were.
Q: How are the games typically paced?
A: This is something newer players are not as accustom to -- the lead metagame. Without team preview, the lead is very important as a trend setter for the game. As someone who used to play it, you would still recognize they are broken down into classes. There are powerful offensive leads that require attention, such as Machamp or Dragonite. Dragonite in particular is a very scary lead that makes having a good lead matchup against it worthwhile. For example, if you have an Aerodactyl, Jirachi, or Flygon lead (which raises eyebrows at the possibility of it being CB as opposed to more common Scarf or Mix sets), Dragonite will be obligated to switch out in most instances. That will allow you to next have to confront it later in the match, likely with it taking SR damage, and probably having a better clue to its set through the scouting of other team members. The danger of Dragonite comes from having a lead that is vulnerable to it (opting for another focus to start the game) and being forced to determine what kind of attack it will fire off without any supporting evidence. Then there are supporting (SR) leads, which are your Aerodactyl, Gliscor, Hippowdon, Heatran, and like leads. Some leads can be either or both offensive and supporting like Heatran, Azelf, Metagross, etc. Ultimately, the lead metagame will determine the initial pace of the match. There is no defined pace of the metagame, much like current OU, it's determined by the team and the player.
This was mostly an appetizer for the way the lead is played. If someone needs a more detailed answer for how the lead metagame works, I can answer that separately.
Q: Are old stalwarts like Jirachi, Tyranitar, Heatran, and Starmie still extremely centralizing?
A: In a word, yes. It's not by any means a necessity that you use them, but there is a reason for their high usage. They are able to fill multiple needs in one team space. Moreover, except in the case of Starmie generally, you can still make use of them in a surprising way. Whether it's through using lesser seen coverage or support moves or the item, which can transform them into a lure with a damage-reducing berry for instance. Most importantly, especially in the case of Jirachi and Tyranitar, you'll need to make sure their various sets are accounted for in the coverage of your team. For Jirachi alone, there are probably 3 or 4 viable CM sets that don't have a single common counter.
Q: What formerly popular Pokemon/sets have become ineffective or even obsolete? What has taken their place?
A: Lumping these two questions together. Probably the most prominent example is Forretress. It was once a premier Spiker with tools to damage Starmie and Rotom, but their sheer prominence in addition to increasingly reduced opportunities to set up and support make it a less desirable choice in general for DPP. There isn't a particular replacement for Forretress in the metagame. Skarmory is still a premier Spiker that is still very effective in thanks to its reliable recovery and phazing. This mostly represents a shift in mindset for the player base. Of course, Roserade still provides a similar alternative with more specified coverage.
To give another example, in terms of sets. Jirachi was at one time commonly seen with a Wish CM set with two coverage moves. That's shifted to being more commonly spotted using more SpA and Spe investment with three coverage moves, which is commonly seen with Psychic, Grass Knot, and HP Ground, but not restricted to using only those moves of course.
Q: More generally, how does one practice any past generation? While old gens show up in a lot of major Smogon tournaments, to say these are inaccessible for the vast number of PC members would be an understatement, and a cursory glance at their respective ladders on Showdown suggests that the ladder is practically useless for finding even mid-level games on even a semi-consistent basis. How do you overcome this?
A: All it takes is some initiative. The ladder on PS is a bit underutilized. It lacks top level competition, though there are a few players that have some talent. There's something to be gained from playing against any level of competition. Outside of the big tournaments, it's probably unlikely to face anyone of top level talent, which is unfortunate. Participation in those is important if you want to join those ranks. The fundamentals can be honed playing against anyone, though. Unless you can go undefeated on ladder, there is value to be had from playing those games to solidify yourself when the bigger challenges arise.
