First off, good luck at the interview. Here are my quick thoughts FWIW:
1. Insurance as a whole is a terrible, commodity business although there are some niche areas of the P&C business like Markel's Excess & Surplus lines that seem to make money over time
2. Combined Ratios tell the first half of the story. (Claims + Operating Costs)/Premiums= Combined. Most insurers run combined ratios north of 100% (ie they lose money on the underwriting business) and then hope (and often pray) that they make money on the investing side via the float.
3. The reserve developments tell the other half of the story. Insurance, like most businesses, is a tug-of-war between the balance sheet and the income statement. Because of the mismatch between financial statements, typically issued annually, and often longer lived insurance policies, an insurer can make their financial statements say whatever they want in a given year. As a result, the change in the reserves over time is a key metric to watch. If the insurer was conservative in the first place, they should be releasing reserves over time ie they put too much money in the piggy bank to pay future claims and so they get to take some back out and put it into their (the shareholder's) pockets.
4. Reinsurance is more commoditized than the traditional P&C given it's low barriers to entry (at least from outside of the US),