A Looted Wagon is a Heavy Support option for your Ork army. I think they're awesome, but not many people agree with me. Let's take a closer look at this unit.Operated by typical Boyz, the BS is 2. Armour is F:11, S11, R:10. It's not great, that's for sure. Especially compared to the likes of a Battlewagon or a Deff Dread.
Why, then, should anyone want one? Well, I can think of 3 reasons.
1.) The Boomgun. This is the only vehicle that can take a Boomgun, and it's the best gun in the army. 36" range, S8, AP3, Ordnance 1, Large Blast. It beats the Battlewagon's Killkannon with both a better strength and a longer range. That's a scary gun. This is what happens when you Imperials bring your game-treads and blow the smithereens out of some Boyz. Some Mek on a hill points at your shiny tank and drools "I Want."
2.) It's cheap. Just the wagon alone is 35 points. Give it a Boomgun and it's 105. Add a 'ard case and it's 115. That's really all you need. Sit that bad-boy off a ways and let it bombard them from afar. Bring along some other scary units to get close to your opponent and keep his/her focus (like a Battlewagon or a Deff Dread), and all the better.
3.) Alternative transport. It's transport capacity is the same as a Trukk (given you don't take the Boomgun)... and it costs the same as a Trukk. It may not be Fast like a Trukk, but it has better armour and doesn't have "Ramshackle" like a Trukk. It's a tough choice taking a Looted Wagon as a transport, since it will take up a Heavy Support slot, but if you want to mechanize your army (i.e. Speed Freekz), some units aren't allowed dedicated transports; this might allow you to take a unit of Tankbustas or Burna Boyz and not leave them behind to footslog. They can just hop in the Wagon. "Another thing that worked relatively well for me was a Looted Wagon with Skorcha carrying a squad of Burnas. The Skorcha rarely got to fire, but it scared enough people to make them want to blow it up, and by the time they did I either destroyed them with my burnas in shooting or held off on shooting and rushed in with power weapons."(Thanks Kevin of Terran Forge) Unlike the Boomgun, a Skorcha doesn't remove your transport capacity, allowing for an interesting combination.
The downsides of a Looted Wagon
Look at the thing; it's busted up. It's alien technology and it's been broken at least once already. She's got some bugs.
Low Armour for a "tank." Fluff-wise it makes a kind of sense. She's already been mistreated by the Tankbustas, supposedly. It won't stand up to much. Hopefully, this is offset somewhat by the range of that Boomgun. Don't go tank-shocking with her; leave that to your Deff Rolla Battlewagons. Also, taking a 'ard case for 10 points will get rid of that "Open-Topped" rule, allowing you a little more resilience.
"Don't Press Dat!" Fluff-wise, this one's there for the alien technology part. At the beginning of every turn, you roll a d6 to test for this. A 2+ means "business as usual." A roll of 1 means that the Wagon must move directly forward as far as it can (12") as "the Orks inside get carried away." ... see, it's little rules like that that make me love the Orks (Shokk Attack Guns also rule for the same reason). Yeah, it's a pain, but your trade-off is a friggin' Boomgun!
Upgrades
There are lots of upgrades, meaning that your Looted Wagon can quickly become very expensive. Only pick the ones you need, keep your points down, and your Looted Wagon will have a better chance of earning her keep.
Main Weapon: You can choose between a Boomgun (70 pts) or a Scorcha (15 pts). You already know which one I like.
Secondary Weapons: You can take up to two of these: Big Shoota (5 pts), Rokkit Launcha (10 pts)
Auxiliary: You can take any of these. This is where things can really add up.
'ard case makes you more resilient.
Red Paint Job makes you go faster.
Grot Riggers can repair "Immobilized."
Stikkbomb Chukkas give disembarking units Stikkbombs
Armour Plates treats "Crew Stunned" as "Crew Shaken" (good if you need to keep moving)
Boarding Plank helps you hurt other vehicles with an embarked unit.
Wreckin' Ball is a big toy for hurting other vehicles/units.
Reinforced Ram allows you to Tank Shock
Grabbin' Klaw attempts to immobilize nearby enemy vehicles.
'ard case is a good one to take no matter what. Paint job, riggers, chukkas, plates are all great for beefing up a Transport. If you're taking the Boomgun, it doesn't matter about the speed, the immobilize, Crew Stunned, or disembarkers (you won't have any). The plank, ball, ram and klaw are all toys. Take 'em if you like 'em, by all means ... but they're not necessary.
Compared to a Battlewagon
Battlewagons are awesome too, don't get me wrong. A Looted Wagon with a Boomgun is more of an Artillery unit than a Battlewagon. If you're used to IG, think of the Looted Wagon as a Basilisk and the Battlewagon as a Leman Russ. They're both useful, but in different ways. A Looted Wagon is much more fragile, yet has a more powerful gun. The Battlewagon is meant to be in the thick of things, tank-shocking and firing off that Killkannon like it's trying to be a Land Raider or something. The Looted Wagon is also the poor Ork's Heavy Support. With a Boomgun, it's only 105 points. A Battlewagon with Killkannon is 150. That's an extra 45 points. What can that buy you? Well, another Killa Kan... or another Deffkopta... or another Warbiker/Warbuggy/ 3 more Stormboyz/A Trukk/16 Gretchin/7 more Boyz/4 more Kommandos/3 more Lootas/3 Tankbustas/3 Burna Boyz/Another Meganob/2 more Nobz or a Big Mek. In an Ork army, 45 points is a lot.
OK, all that having been said, here are a couple highlights of the model pictured, starting with my "Stikkbomb Chukka"
Ever since the "Inc'dent on Diss'poyntmint Ridge" ol' Gob-Stompa don' let the Boyz carry Stikkbombs inside the Looted Wagons. They gotta sling 'em outside the chuckin' window. I assembled this guy before the codex came out, it had been sitting on my desk for a while. If I had waited, I wouldn't have had a Stikkbomb Chukka on my Boomgun-Wagon ... as there's no passengers to pass the benefit to, so it's purely cosmetic on this guy.
Also, since I am collecting an Evil Sunz army, I will take Red Paint Job to keep things fluffy. When my Lootas go a little crazy with pulling the wrong levers they'll lurch forward an extra inch. ;)
I think my favorite detail on the wagon is the pistol mounted to the side of the turret:
One of the Meks stuffed a grot in that side compartment. His job is to keep shooting that gun (even though he can't see anything). When the Boyz hear he's out of ammo, they open the hatch and pour some more bullets into the bucket. The belt-feeder takes them to the grot-blasta. 
'ave a nice day!
