One of the better Halo/Mass Effect crossovers, but still isn't the greatest.
The Last Spartan is a good fic. It has solid writing and an interesting premise, but it really shines in the characterization department. It has the best depiction of Master Chief I've ever seen. It even does a good job detailing Chief's reactions to being thrust into an entirely new galaxy.
Unfortunately, that's where the greatness ends. The crossover method is like oil and water: They don't mix. The Halo cultures are completely out of character. Granted, a lot could change in one hundred years, but they're just too out of character. This is especially jarring considering how well he does other characters. Furthermore, I just can't buy that Master Chief survived in cryo for one hundred years. Nor can I buy that the UNSC would simply give up all their advanced technology
Basically, characterization is great, world building is awful. It's up to you whether you can look past the flaws. Overall, it's at least worth a look. I give it 8/10.