New Players, this is a very solid option for your first AEG. For those that are researching, I know that there are a lot of mixed feelings about the Sportline series. I'm going to try and focus on my personal observations and stick to the facts. As you read on, understand that this review is on the 2010 model so you may find some differences from you read elsewhere. (the Sportline series was introduced 2 - 3 years prior)
First off, the construction. There are a surprising number of metal parts on this gun. The inner and outer barrel, RIS system, rear sight, charging handle, and gear box. The body is a thick polymer and is unbelievably sturdy. All pieced together, you have a solid rifle with zero wobble. On the construction side of things, the only negative I found is the Crane Stock. The Crane Stock feels very fragile and from my early inspection was the only piece that wobbled a little. The battery compartment is very difficult to remove and takes away (albeit only a little) from the overall quality of the gun.
While I have only opened the gun enough to inspect the inside briefly (I was anxious to test fire) I can tell you that the descriptions listed on the ASGI site are pretty spot on. The M15A4 Sportline has a Version 2 metal gear box and cylinder, metal inner barrel, but what surprised me the most was the wiring. The battery wiring within the crane stock is sleeved in a thick rubber "pigtail" chord. This lends to very easy insertion of the battery and keeps it solidly in place.
If you are reading this review, there is something you need to know. There are two product pages to purchase this rifle. The page you are reading is the gun ONLY. The reason I bring this up, is that purchasing the gun by itself you will not get a battery or charger included. I would suggest purchasing the (Sportline/Value Package) as this comes with a battery and charger. The RIS/Crane Stock Sportline requires a Crane Stock battery and it will save you some delivery headaches in the meantime.
Overall, I give the CA M15A4 RIS Sportline a respectable nod and an 8 out 10
Metal outer barrel
Metal inner barrel
Metal V2 Gearbox
A GREAT option for a starter AEG
Poor Crane stock construction (my opinion)
No included battery or charger
Very little else