Great RL players would be great players in any era, regardless of weather they play the game now, or in the past. I do think the positions some players play, or played would be different because the skill set required in certain positions was very different then, and it's very different now.
As for the overall standard, I don't think the standards or skills have dropped at all. Where I think the game has changed is that players today have a lot less time on the ball, and less space to accurately execute there skills. When you look at the game from the 20th century what's noticeable is how 'broken' the defensive lines were, and how few players were involved in the tackle. Also, the likes of Andy Gregory used to crab across the field and looking for gaps, I think if he tried that so often in todays game he'd more often than not got smashed by the advancing defence. I'm not saying that he wouldn't have been a great player now, he was a very skilful player, but I do think he would have to adapt his game significantly to succeed, not to mention his lifestyle.
Personally, I love the game as much as ever. It's totally different to when I started watching it, but that doesn't mean it's not fun to watch. Granted there's some dross served up each week, but that's ALWAYS been the case in any sport.