I think I'd extend transitional from PS1/N64 all the way up to PS3/Wii. The first gen 3D consoles have a definite transitional jank to them that I can understand acknowledging, but it's also a period of industry transition where the meaning of AAA games changed from smaller teams and tech focus to huge teams and content focus, and the last era before online play, patches, and microtransactions became common.

I mostly consider PS3/Wii to be early modern gaming. It's not quite modern modern, but most of the components were already there. Horse armor came out half a year before they were released, a harbinger of things to come. Informal LAN parties (ie outside of a gaming cafe) were already seen as an anachronism by that time. Server multiplayer still was a thing, but they were going to compete with matchmaking. Arcades still held on with fighting games like Marvel and DDR, but it had long since been eclipsed by consoles and PC. Plants vs Zombies and Farmville came out around this time. eSports was already a thing by this time with SC2, which of course grew out of SC1. MOBAs ultimately came out of a WC3 mod which was inspired/based on a BW mod.

I'd also probably cut retro into two periods somewhere around 1986. Even on the NES, where this was mid-generation, almost all the fondly remembered games came out from 1987 onwards.

I didn't want to make the post too long, but I split retro gaming into three parts:

Archaic gaming: Basically weird experiments like that tennis game being played on an oscilloscope or some ancient RPG from the mid-70s. Pong could go here, which apparently led to Pong clones and a subsequent Pong crash. In this era, purely electronic games had to share space with electro-mechanical games.
Early retro gaming: Everything from the release of Space Invaders up to the videogame crash of 1983. All your arcade classics like Breakout and Pac-Man go here. This was the era of the Atari 2600.
Late retro gaming: This is post videogame crash with the rise and complete dominance of Nintendo. Most gaming franchises began here. Franchises like Mario or Zelda or Final Fantasy. On a more negative note, this is where "gaming is for boys" began because after the crash, Nintendo sold gaming as "toys for boys." I honestly think you could trace Gamergate back to Nintendo's marketing decision. Something like the development of Ms. Pac-Man, an early retro game, was a glimpse of what could've been.