These are Year One values, Thunderlord Year Two has changed quite a bit.
Thunderlord is a high-Impact Machine Gun with good Stability (41), good Range (34), and an overall great balance of stats. Thunderlord's main feature is faster & more accurate shots the longer you fire. It even has a hidden talent: occasional AOE Arc-damage blasts on a kill.
As mentioned above, it's primarily known for being so well-balanced – unusual for a Machine Gun with such high Impact. Thunderlord boasts a very respectable 38-round clip and has a few notable talents (Field Scout, Perfect Balance). Ultimately, the perks are just icing.
In PVE, Thunderlord is very popular for Arc Burn Nightfalls & Heroics (with good reason!) With a 60-round clip (Field Scout) then switching to Perfect Balance, you've got a highly-accurate, Arc burn boss-killer. (Moments like this come to mind.)
For PVP, it's a divisive topic. You can't spend the ammo to trigger its Exotic perk, so you're left with a well-balanced, high Impact Machine Gun. Good in its own right, but can be substituted by Deviant Gravity-A if you have another Exotic in mind.
Of course, Thunderlord's best selling point is that it looks impressive and has an amazing, distinct ping!ping!ping! sound. You always take notice when a Thunderlord is being fired nearby. It's the sound of Guardians getting things done – and doing it in sky-cracking style.
- Excerpt from "'Should I Buy It?' – Thunderlord & Other Exotics"