Looks like 2 years well spent!! Nice job man!! Especially for a first build! You should be so proud of yourself. You've really done a nice job.
We can always do more I suppose, so let me think of what stands out from my quick analysis that might be able to be improved.
- It's never a bad idea to get lots of references. 343 has an official "the Rookie" cosplay guide. It's a good resource with loads of high definition reference images. Here's a link: Official 343i Cosplay Guide: The Rookie
- Upon comparing your images to those reference images, I'm thinking the relative size of your helmet is off. From what I can tell the in-game ODST's helmet comes pretty far down close to the large straps that go over their shoulders, whereas your helmet only comes down to the bottom of your chin. I think this, along with your less-padded shoulder straps in that first image make the gap between your helmet and armour seem a bit long. Perhaps creating a larger helmet and/or adding some padding to those shoulder straps will help those proportions. I can see you have longer hair though, which might make it difficult to get the helmet to sit lower.
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- Your leg armour looks great! The sizing is excellent from what I can tell. The only think you're missing is some boot covers.
- There are a few spots on your under suit near your abdomen that aren't covered by armour which leaves a bit of a gap in the detail.
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This certainly isn't a major thing, but since I'm looking for anything that could (not necessarily should) be done better I thought I'd mention it. I'm not certain how this could be improved, but my best thought is to see what other ODST's have done to add depth to that area. In all honesty, I think most people just wear flat black like you've done. After looking at the ODST's in the Canadian Regiment (for some reason we have a LOT of them), I can see most of them don't do anything revolutionary in regards to this.
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The ODST's in those pictures from right to left are PaiganBoi, Ryujiro, Shane (idk his @), Schankerz, NewBrody, and the last two I only know their real names, not their @'s. Knowing their forum names will help you if you decide to look through their build threads.
That's all I can see at the moment. Now, I've never made an ODST cosplay so my advice is only worth what you paid for it. I have a feeling you've already made a list in your head of things you were thinking of improving, and are looking for some reassurance that they're worth tackling. I hope I touched on all the things you were hoping I was. If there's anything specific you'd like feedback on, I'm happy to take a closer look at it!