If you're looking for quality in hentai that stuff nowadays can't top, I'd suggest
- G-Spot Express (people may disagree with me but I love the style that series had)
- Mezzo Forte (although there are like only 2 scenes, but they're amazing, the rest of the show itself was pretty good even without the erotica)
- Maid in Heaven
- Viper series videos (Lingerie) (titled with colors), these are videos of the in-game animations and sounds from the viper series, if you liked Viper GTS, you can check out where they got it from
Stuff not too long ago that isn't bad:
- Resort Boin (this is one of my recent favorites, colors are a lot more brighter compared to the ones above but the scenes are pretty enjoyable)
- Kanojo x Kanojo x Kanojo (artstyle similar to Resort Boin)
If you want variety of scenes within a series, take a look at Stringendo and Accelerando, the ones made after Yuki Seto's mangas. However, the quality drops after each sequel which I presume would be because they were just milking the series for cash and reducing their budget.