JoJo no Kimyou na Bouken (TV), Ushio to Tora (TV) Recommendations
While the manga of JoJo is seen as one of the forefathers of standard battle manga/anime, Ushio to Tora's manga is seen as one of the forefathers of youkai battle manga/anime.
Both of these anime have an old-school feel to them and are re-adaptations of manga that got sub-par OVAs years ago. Also, they both have great action scenes and can get a bit brutal at times (JoJo especially).
Both anime should be watched before other mainstream shounen because they have influenced those mainstream shounen. At least, that's what I think.
Both are proper modern adaptations of oldschool mangas, that adapt the whole source material.
Both have straightforward story and are quite brutal.