I have owned and used my Tippmann Sl-68 II since 1996. During that time my marker has seen very heavy use by me and others. There are many things that I like about the marker and a few things that I don't. This review will cover my experience with the marker in detail. 

I prefer the SL-68 II over other Nelson based pump paintball guns for several reasons.

Locking Bolt:  The bolt locks in place after the marker is cocked. This prevents double feeding and creates a stable platform to shoot from since the slide does not move. I owned a Phantom for two years and tried to play with it many times. However, I could never get used to the pump arm moving freely after the gun was cocked.

Iron Sight: The SL-68II has iron sights, and they work. You really can hit what you aim for with this marker.

Autotrigger: The marker is equipped with an auto trigger. This allows you to hold down the trigger and simply pump the marker. The gun will fire each time the bolt goes to the forward position. This is extremely useful when you are in a tight situation and need additional firepower. A ref actually warned me once for overshooting an opponent while bunkering him. Just be careful not to chop a ball when using the auto trigger though. 

Cleaning:  The marker has an access port on the side of the gun. This allows you to run a squeegie through without removing the barrel.

Dislikes: The only thing that I guess I can really complain about is the pistol grip. I am 6ft 3inches tall and  have large hands. The pistol grip is slightly too small for my hand. Its not a big deal really, and does not affect my ability to use the marker. However, I do notice it, especially as the day goes on. The only other issue is that you cannot really upgrade the marker and after market barrels are hard to find. You can find them, its just not easy. That's why I had to modify one to fit.

Overall Observations: The gun is extremely accurate with the 16 inch Smart Parts All-American barrel that I modified to fit the gun. Head shots are no problem even at extended range.  I have played with, and owned many guns since I began playing in 1986. The SL-68II is my favorite, bar none. Don't get me wrong, I enjoy a good fast shooting electro just as much as the next guy. However, there is a certain satisfaction I get from playing at a disadvantage and making good accurate shots to eliminate my opponent. 

I have found that my gun operates best on C02. I have tried compressed air from a preset tank. However, I was not able to get the marker to shoot more than about 220-230 feet per second. I have heard of others having the same problem. Its no big deal really, the gun is quite consistent with Co2 anyways.

Playing Pump in General: Playing pump is not for everybody. You will either love it for the challenge, or hate it because you are at a disadvantage. Most people that try pump paintball fall into one of those catogories and rarely in the middle. I have experienced the usual " why would you want to play with that", and all of the quiet comments in the staging area when players think I can't hear them. However, it never comes from the guys who have played against me before. They have learned not to under estimate me or my marker. They have learned to watch for me, and have grown to respect me. There is nothing like overhearing them as they warn others not to underestimate the guy with the pump.

Conclusion: I hope that this guide has been helpful. I hope that you will try playing pump if you have never done it before. Buy a used gun off of ebay and give it a whirl. You can play with just a pump, or break it out at the end of the day when your paint is running low. You can always sell the gun if you don't like it.  Don't be afraid to play at a disadvantage and get your rear handed to you a few times. It will make you a better player even when you go back to your electro.