http://www.tesnexus.com/downloads/file.php?id=2536 does a lot to make the game gorgeous. You get better looking and a greater variety of weather types that make the sky look awesome, great color variety for summer days vs. winter days and sunrise and sunset, the moons look cooler. Also it rescales the vegetation - trees are realistically taller etc. making the forest a LOT better. You even get birds and insects flying around.
And you get bugs too! But not of the insect variety, instead of immersion breaking, shouldn't use the mod variety. Don't use the weather system, Natural Weather, of Natural Environments. I suggest you use another weather mod that's not bug-ridden, such as
http://www.tesnexus.com/downloads/file.php?id=18305. It's by far the superior weather system available at this time and for the foreseeable future. If you decide against All Natural for whatever reason then I'd suggest
http://www.tesnexus.com/downloads/file.php?id=16544 as a nice alternative.
There are other alternatives for vegetation and water too.
http://www.tesnexus.com/downloads/file.php?id=23783 is excellent and has multiple scaling options. As for water mods just search around, there are many available. You're bound to find one that suits your tastes.
The only part of Natural Environments I suggest you use is Natural Habitat. Since there is not really anything out there to replace that aspect and it does the job very well.
Check out
http://www.gamesas.com/index.php?showtopic=960829 for a great selection of what's available.